Bookmarks
Importable bookmarks export
Software & Dev
AI / ML
- Aider — AI pair programming in terminal
- Open-source AI coding assistant you run yourself. Great for experiments.
- Anthropic — Engineering blog
- How they actually build Claude: agents, evals, systems, safety.
- Anthropic — Research
- Constitutional AI, interpretability, RLHF, evaluations. Read the papers.
- Anthropic Docs (API)
- API reference, prompt engineering guide, tool-use and MCP docs.
- Anthropic prompt engineering guide
- Practical prompting: XML tags, examples, chaining. Very actionable.
- ar5iv (arXiv to HTML)
- Renders arXiv papers as readable HTML with proper equations.
- arXiv cs.AI recent
- The AI subset of arXiv.
- arXiv cs.CL recent (NLP/LLM)
- Computational linguistics and LLM papers.
- arXiv cs.LG recent
- The ML firehose. Filter via HF Papers when you can.
- BAIR Blog (Berkeley AI Research)
- Research summaries from Berkeley's AI lab. Strong on RL and vision.
- Berkeley CS285 (deep RL)
- Free advanced deep RL course. Assignments implement real algorithms.
- Berkeley LLM Agents course (Gorilla)
- The Berkeley LLM agents course. Free, current and practical.
- Building Effective Agents (Anthropic)
- The clearest free explanation of workflows vs agents. Read this.
- Cohere for AI blog
- Technically strong posts on embeddings, RAG and evaluation.
- DeepLearning.AI short courses
- Free 1-2 hour courses on agents, LangChain, transformers, RAG.
- DeepMind blog
- AlphaFold, Gemini, agents. Accessible write-ups of frontier work.
- Distill
- Interactive, beautifully explained ML ideas. A gold standard explainer.
- EleutherAI
- Open, non-profit GPT research collective behind The Pile.
- fast.ai — Practical Deep Learning
- Top-down, free, project-based deep learning. Best intro if you build.
- Gemma / open models on HF
- Google's open models, plus strong fine-tuned variants from the community.
- Google AI blog
- Google and DeepMind product and research announcements.
- Google PAIR — People + AI Research
- Human-centered AI design, explainers and toolkits. Great for product AI.
- Gradio — build AI demos fast
- The standard way to ship an AI demo UI. Free and open source.
- Groq blog
- Fast LLM inference on custom hardware. Good performance engineering.
- Hugging Face — Daily Papers
- The best ML paper feed, with community explanations. Daily.
- Hugging Face — Learn (free courses)
- Free courses: NLP, deep RL, audio, CV, LLM course, agents. Excellent.
- Hugging Face — LLM Course
- Free course: APIs, RAG, agents, fine-tuning, quantization.
- Hugging Face — smol-course
- Tiny hands-on course to fine-tune and use open LLMs. Beginner friendly.
- Hugging Face — the hub
- Models, datasets, Spaces and docs. The center of open ML.
- Hugging Face — Transformers docs
- The best practical library docs in ML. Learn from the notebooks.
- Import AI (Jack Clark)
- Weekly synthesis of AI research, policy and compute. Sharp.
- Interconnections (One Useful Thing)
- Ethan Mollick on how to actually use LLMs effectively.
- JAX documentation
- Composable transformations for ML. Learn if you need custom accelerators.
- Kagi / independent AI search
- Kagi's blog posts on building a search engine with LLM reranking.
- Karpathy — A Recipe for Neural Networks
- Building a neural net in pure Python, explained. Gold.
- Karpathy's Zero to Hero course
- Free, complete neural-network course: from backprop to GPT. Start here.
- LangChain
- The most common LLM app framework. Learn the primitives, then the abstractions.
- Latent Space podcast
- The best AI-engineering podcast: infra, evals, agents, interviews.
- llama.cpp
- Run quantized LLMs on CPU/laptop. Popular and fast.
- LlamaIndex
- Data framework for connecting LLMs to your documents. Great RAG docs.
- llm.c (Karpathy)
- LLM training in raw C. See what frameworks hide from you.
- LM Studio
- Friendly GUI for local models, with a local HTTP API. Great for tinkering.
- MCP documentation (Model Context Protocol)
- The open protocol for connecting LLMs to tools and data. Learn it early.
- MCP servers directory
- Reference MCP server implementations to learn from.
- Meta AI blog
- Llama, SAM and FAIR research write-ups.
- Microsoft Research Blog
- Deep technical posts on models, systems and responsible AI.
- Mistral AI news
- Open-weight models and technical notes. Read the open releases.
- MLflow
- Open-source experiment tracking and model lifecycle management.
- Modal blog (AI infra)
- Practical GPU and AI infra: serving, batching, cold starts.
- nanoGPT (Karpathy)
- GPT in ~300 lines. Read the code to demystify transformers.
- NumPy / numerical computing docs
- The foundation of most Python ML. Reading these helps you write faster code.
- Ollama — run LLMs locally
- One-command local LLMs. Best on-ramp to running models yourself.
- OpenAI Cookbook
- Practical recipes for prompting, RAG, tools, evals. Free.
- OpenAI Realtime / agents guides
- API guides for building agents, tools and realtime features.
- OpenAI Research
- Research index: GPT, alignment, o-series, and more.
- OpenAI Spinning Up
- Free rigorous RL primer (DQN, PPO, SAC). Still the best RL tutorial.
- Our World in Data — AI
- Data-driven visuals on AI progress and impact. Great for intuition.
- OWASP Top 10 for LLM Applications
- Prompt injection, RAG poisoning and other LLM app security risks.
- Papers with Code
- Papers linked to runnable code and leaderboards. Winding down but useful archive.
- Prompt Engineering Guide (DAIR.AI)
- A free, well-organized guide to prompting techniques and papers.
- PyTorch tutorials
- The main PyTorch learning path. Start with the 60-minute basics.
- Qwen (Alibaba) models & blog
- Strong open-weight models with good releases and blog posts.
- Reinforcement Learning: An Introduction
- Sutton & Barto's definitive free RL textbook, 2nd edition.
- Replicate blog
- Open model demos and how they serve models at scale.
- scikit-learn user guide
- The classic ML algorithms with clear, practical examples.
- Simon Willison's Weblog (LLM tags)
- Daily notes on LLMs, RAG, agents and building with them. Superb.
- Stanford AI Index Report
- Annual state of AI: benchmarks, costs, incidents. Free report.
- Stanford CS224n (NLP)
- Free NLP course materials: slides, code, videos.
- Stanford CS231n (vision)
- Free, excellent deep learning for computer vision with assignments.
- Streamlit — data/AI apps
- Turn a Python script into a shareable app. Free and open source.
- The Gradient
- Narrative essays on the science and philosophy of machine learning.
- The Illustrated GPT-2
- How a real LM processes text, step by step. Excellent.
- The Illustrated Stable Diffusion
- Clear visual explanation of diffusion models. Great intro.
- The Illustrated Transformer
- The clearest visual explanation of attention and transformers.
- Together AI blog
- Open models, fine-tuning and inference optimization write-ups.
- vLLM
- High-throughput LLM serving. Learn from its optimization write-ups.
- Weights & Biases docs (free tier)
- Experiment tracking, sweeps and model registry. Good free tier.
Android
- Android app bundles
- AAB format, dynamic delivery and how Play Store serves your app.
- Android architecture guide
- Recommended layers, UDF, ViewModel, repository. The canonical doc.
- Android build system docs
- Variants, dependencies, signing and CI for the Android build.
- Android code snippets
- Small copy-pasteable snippets for common Android tasks.
- Android Developers (official)
- Main hub: guides, references, training, release notes.
- Android Developers Blog
- Official blog: new APIs, best practices, case studies. Great signal.
- Android Developers YouTube
- I/O and AndroidShow talks plus deep technical sessions. Free.
- Android on Reddit (r/androiddev)
- Active community: news, libraries, architecture debates, job talk.
- Android privacy & security hub
- Permissions, data safety and secure defaults. Required for shipping.
- Android security best practices
- Store keys in Keystore, not SharedPreferences. Classic mistakes.
- Android Studio Live Edit (experimental)
- Hot-reload style tooling to keep your inner loop fast.
- Android Studio release notes
- New IDE features: profiling, Compose previews, AI Assistant.
- Android Vitals (performance)
- The metrics that matter: startup, jank, ANRs, and how to fix them.
- Android Weekly newsletter
- Weekly roundup of Android news, articles and libraries.
- Android: reduce app size guide
- Size, startup and battery guidance. Very practical for shipping.
- AndroidX release notes
- What's new and stable across every AndroidX library.
- AOSP code search
- Search and read the entire Android platform source online.
- AOSP source download
- The real Android platform source. Reference when docs are unclear.
- Baseline Profiles
- Modern AOT warmup. The 2024+ way to launch faster.
- Coil (image loading)
- Kotlin-first image loader built on coroutines and OkHttp.
- Compose architecture guidance
- UDF, ViewModel and state hoisting. The right way to structure Compose.
- Compose BOM
- Align your Compose library versions with one BOM. Good hygiene.
- Compose codelabs pathway
- Structured Compose codelabs: basics → advanced → architecture.
- Compose documentation
- Deep Compose reference: layout, state, lists, animation, accessibility.
- Compose samples
- Focused samples: layouts, lists, animation, accessibility.
- Data binding / Compose interop
- Migrating from Views to Compose incrementally. Useful reference.
- DataStore (preferences)
- Modern SharedPreferences replacement: async, typed, Flow-based.
- Dependency injection guide
- The broader DI docs plus Hilt testing with HiltAndroidRule.
- Espresso UI testing
- Instrumented UI tests for the View system. Compose has its own tools.
- Glide (image loading)
- The long-standing image loading library. Still widely used.
- Google Developers Blog
- Official Google developer announcements across Android, Flutter, AI and more.
- Google I/O sessions (free replays)
- Biggest annual Android and Google announcements, all replayed free.
- Gradle user guide
- The official Gradle docs. Read when customizing your build.
- Hilt dependency injection
- Google's DI framework built on Dagger. The standard choice now.
- Jetpack Compose
- The modern UI toolkit. The Compose learning path starts here.
- Jetpack Preview for Compose
- Live previews, @PreviewParameter and screenshot testing. Great DX.
- Jetpack Security (crypto)
- Use Jetpack Security, not raw crypto. Official crypto guidance.
- Kotlin coroutines on Android
- Structured concurrency: scopes, dispatchers, Flow. Must-read.
- Kotlin/Android testing recipes
- Local, instrumented and Robolectric testing guidance.
- Macrobenchmark
- Measure startup and jank properly with Macrobenchmark.
- Material Components for Android
- The component library and design guidance for M3.
- Material Design 3
- The official Material 3 design system. Build themes from it.
- Navigation Compose
- Type-safe Compose navigation with arguments and deep links.
- Navigation overview
- The full navigation reference across Compose and Views.
- OkHttp
- The HTTP engine most Android and JVM apps use underneath.
- Paging 3
- Paged lists with Room integration. The modern way to do feeds.
- R8 shrinking & obfuscation
- How R8 shrinks and optimizes your app. Important to configure.
- Rendering & jank
- Why frames drop and how to fix layout, allocation and overdraw.
- Retrofit
- Type-safe HTTP client for Android and the JVM. The default networking choice.
- Room (SQL persistence)
- The recommended SQLite layer, with compile-time SQL checks.
- WorkManager (background work)
- The right way to do deferrable background work on Android.
Architecture
- adr-tools
- CLI to write ADRs as numbered markdown files in git.
- Alistair Cockburn's blog
- Agile in a Nutshell, sculpting, and architecture essays.
- Android architecture samples
- Google's reference samples: MVVM/MVI, clean layers, Compose.
- Applying Clean Architecture to Go
- A concrete walkthrough of Clean Architecture layers in a real Go service.
- Ardan Labs — service-driven design
- Training repo with a clean layered Go layout.
- Documenting Architecture Decisions (Nygard)
- The original ADRs post. Short, worth every minute.
- Domain Event (Fowler EAA)
- Fowler on domain events, event notification and event-carried state transfer.
- Domain-Driven Design resources
- Curated DDD articles, talks and case studies. Great entry point.
- Eric Evans — Domain Language
- Evans on strategic design, bounded contexts, context maps.
- Feature-Driven Design (Scott Cohen)
- A modern practical cousin of DDD by the author of the Alchemist book.
- Flutter clean architecture samples
- Community Flutter examples incl. clean / feature-first layouts.
- Flutterpedia (community wiki)
- Huge community-edited Flutter knowledge base.
- Go Clean Architecture template
- Opinionated Go layout: handlers → usecases → repositories.
- Hexagonal Architecture (Cockburn, original)
- The 2000 post that coined ports & adapters. Definition with diagram.
- MADR — Markdown ADRs
- A fuller ADR template with a status lifecycle. Good default.
- Microservices (Fowler & Lewis)
- The essay that popularized microservices. Free, definitive.
- microservices.io patterns
- Richardson's catalogue: sagas, outbox, CQRS, API gateway, idempotency.
- Monolith to Microservices (Fowler & Humble)
- Fowler and Humble on decomposition. Browse the free online chapters from the books page.
- MonolithFirst (Fowler)
- Fowler's counter-essay: start as a monolith.
- Now in Android
- Google's flagship Kotlin app: production-grade modern architecture.
- Onion Architecture
- Jeffrey Palermo's onion variant of Clean Architecture.
- Patterns of Enterprise Application Architecture
- The free online P of EAA catalogue. Core data-modeling patterns.
- Ports & Adapters revisited (Cockburn PDF)
- Cockburn generalises hexagonal architecture into component + strategy. Free PDF.
- The Clean Architecture (Robert C. Martin)
- The canonical long-form post defining Clean Architecture. Start here.
- The Clean Coder blog
- Uncle Bob on SOLID, architecture, design and agile, endlessly.
Big tech blogs
- Adyen Engineering
- Payments infrastructure and machine learning at scale. Great posts.
- Airbnb Engineering
- Design, infra and ML at scale. On Medium, but worth following.
- Alpin Schwarz (Fly.io data infra)
- Data systems, Postgres, ClickHouse, modern OLAP. A standout blog.
- Atlassian Engineering Blog
- Distributed systems, incident response, and building at scale.
- AWS Architecture Blog
- Monthly deep dives on architecture, serverless and AWS patterns.
- AWS Builders' Library
- The gold standard on distributed-system reliability. Every pattern is free.
- Azure Blog (Microsoft)
- Cloud architecture and Microsoft's open-source pushes.
- Bolt Engineering Blog
- Payments, risk and engineering craft. Nicely written.
- Booking.com Tech Blog
- Large-scale Java and infrastructure. Practical engineering posts.
- Brandur Leach (databases)
- Data modeling, Postgres and database internals essays. Superb and deep.
- Canonical engineering blog
- Ubuntu, Linux and infrastructure engineering from the Ubuntu team.
- Canva Engineering Blog
- Real-time collaborative editing, scaling, and design-tool internals.
- Cloudflare Blog
- Networking, security, edge, Rust and Go internals. Arguably the best.
- Cockroach Labs Blog
- Distributed SQL, consensus, and globally-consistent DB internals.
- Coinbase Engineering Blog
- Crypto infrastructure, matching engines and on-chain systems.
- Datadog Engineering Blog
- Observability, monitoring, and building the product you use to measure.
- DigitalOcean engineering
- Cloud infrastructure and how they build their platform.
- Dropbox Tech Blog
- Storage, sync, magic pocket, and how Dropbox runs its stack.
- Duolingo Engineering Blog
- Feature rollouts, experimentation and mobile engineering at scale. Fun writing.
- Elastic Engineering blog
- Search internals, Lucene and distributed data. Good explainers.
- Expedia Group Tech Blog
- Travel tech at scale: search, pricing, personalization.
- Figma Engineering
- Multiplayer sync, CRDTs, WebGL and browser engineering. Very deep.
- Fly.io Blog
- Hosting, networking, and running our own metal. Great depth.
- GitHub Engineering Blog
- How GitHub itself is built: MySQL, Git, Actions, security.
- GitLab Handbook (engineering)
- Transparent engineering practices. The best public handbook, period.
- Grafana Labs blog
- Observability, metrics and dashboards. Practical recipes.
- HashiCorp engineering blog
- Infrastructure tooling, Go, and distributed systems practice.
- LinkedIn Engineering Blog
- Kafka origins, streaming at scale, and how LinkedIn hires. Solid.
- Meta Engineering Blog
- Infrastructure, storage, ML infra, and FB engineering culture.
- Mixpanel engineering blog
- Analytics data infrastructure and query engines. Interesting internals.
- Netflix Tech Blog
- Streaming at scale, chaos engineering, data platform, personalization.
- Pinterest Engineering
- Recommendation systems, MySQL sharding, and visual search.
- Plaid Engineering Blog
- Data infrastructure, ML, and developer experience. Good writing.
- PlanetScale / Vitess blog
- MySQL at scale, sharding, schema evolution. Excellent database writing.
- Reddit Engineering
- Postgres at scale, caching, and the joy of legacy systems.
- Segment engineering (Twilio)
- Data pipelines, CDC, and high-volume ingestion. Solid writing.
- Sentry Engineering Blog
- Error tracking internals, performance, and event pipelines.
- Slack Engineering Blog
- Messaging, infra, and how Slack built for reliability. Strong writing.
- Spotify Engineering Blog
- Personalization, data, and mobile engineering at Spotify.
- Stripe Engineering
- Payment systems, API design, and infrastructure. Very high craft bar.
- Supabase Blog
- Postgres, realtime, and building an open-source BaaS. Great content.
- TiKV blog and deep dives
- Raft and consensus plus the guts of TiKV. Advanced but superb.
- Uber Engineering
- Geospatial, payments, matching, and huge-scale migrations. Deep.
- Vercel Engineering Blog
- Serverless, edge, Next.js and web performance. Very current.
- Wise tech blog
- Payments engineering and multi-region financial infrastructure.
- X / Twitter Engineering Blog
- Real-time feeds, ads and infrastructure at X scale.
Compilers
- ACM SIGPLAN blog
- Programming-language research commentary from the community.
- Bjarne Stroustrup's site
- C++ designer's writing on evolution, teaching, and design. Thoughtful.
- C committee papers (WG14)
- C proposals and papers. See where C is heading.
- C++ committee papers (WG21)
- C++ proposals and their status. Reading these reveals the language's future.
- C++ Core Guidelines
- The community's C++ best practices. Great reference for modern C++.
- C++ FAQ (Stroustrup)
- Direct, blunt answers about C++ design and the ongoing evolution of the language.
- chibicc — C compiler in ~10k LOC
- Small, educational C compiler. Very readable C. Highly recommended.
- Clang documentation
- C/C++/ObjC front-end docs: internals, extensions, coding style.
- Compiler Explorer (godbolt.org)
- See generated assembly for C/C++/Rust/Go/... Essential for learning codegen.
- Cornell CS 6110 (Avi Wigderson)
- Strongly-typed intermediate representations and program optimization. Free course.
- Crafting Interpreters (Bob Nystrom)
- Build two language implementations (Lox) from scratch. Free and loved.
- GCC Internals documentation
- The definitive reference for how GCC passes and RTL work. Deep.
- Impala & LLVM tutorials (compilers.dev)
- A growing set of clearly explained compiler internals tutorials.
- Kaleidoscope tutorial (LLVM)
- Build a JIT'd language on LLVM. The canonical LLVM tutorial.
- Language server protocol (LSP)
- The editor-to-compiler standard. Learn it to build language tooling.
- LLVM documentation
- Compiler infrastructure docs. Start with Getting Started and Kaleidoscope.
- Machine learning for compilers (survey)
- Track the research frontier in programming languages.
- Nora Sandler — A Compiler Writing Journey
- Writing a C compiler in Haskell, step by step, with a free book.
- quuxplusone blog (C++ and assembly)
- Marcin Kowalczyk's deep dives into what C++ actually compiles to.
- Regehr's blog (John Regehr)
- Undefined behavior, compiler bugs, UBSan. Sharpest writing on correctness.
- RISC-V specifications (open ISA)
- Open ISA spec, freely readable. Great if you like hardware.
- Software Foundations (Coq)
- Formal verification in Coq, free and rigorous. Very deep but excellent.
- Tiny C Compiler (TCC)
- A small readable C compiler. Great to skim and read.
- TypeScript compiler performance wiki
- How the TS team actually makes the compiler fast. Practical lessons.
- UT Austin CS 380C (Pingali)
- Notes and assignments on modern compiler construction. Free.
- Zig language reference
- A modern systems language with comptime. Excellent reference.
- Zig Learn (free course)
- Free structured Zig course in the browser. Beginner to competent.
Computer Science
- Algorithms by Dasgupta, Papadimitriou, Vazirani (free)
- Free chapters from a respected algorithms textbook. Excellent rigor.
- Analytic Combinatorics (free)
- Flajolet & Sedgewick's classic, free online. Deep and beautifully clear.
- ANTLR — parser generator
- Free parser generator for building compilers. Well documented.
- APEX Calculus (free)
- Free, genuinely excellent calculus textbook. Complete and well written.
- Art of Problem Solving
- Free math forum, books and courses. The best place to get better at math.
- Astropy — astronomy in Python
- Free open-source astronomy library in Python. Excellent docs.
- Babel — compiler
- Free docs for the widely used JS compiler. Well documented.
- Bayesian Analysis with Python (free)
- Free PyMC tutorial book. The best practical Bayesian resource.
- Bayesian Data Analysis 3 (free PDF)
- Gelman et al. The definitive Bayesian textbook, free online. Rigorous.
- BetterExplained
- Free math explanations with intuition first. Very good teaching style.
- Bison — parser generator
- Free GNU parser generator. Standard for compiler construction.
- Can I use
- Free browser compatibility tables. The quick answer to 'can I use this'.
- Carnap — logic course (free)
- Free browser-based logic course with an interactive proof system.
- Computer Networks: A Systems Approach (free)
- Peterson & Davie's networking textbook, free online. The best modern one.
- Coq theorem prover
- Free open-source proof assistant with excellent tutorials.
- D2 — declarative diagrams
- Free modern diagram-as-code language. Cleaner than Graphviz.
- Dive into Deep Learning (free)
- Free interactive deep learning textbook with runnable code. Outstanding.
- First Contributions
- Free repo that walks you through your first pull request. Great onboarding.
- FLAME — Interactive Logic Foundations
- Free interactive proof assistant in the browser. Easiest way to learn formal logic.
- Good First Issue
- Free directory of beginner-friendly open source issues. Perfect starting point.
- Google Summer of Code
- Free paid internships contributing to open source. Highly competitive, worth it.
- Graphviz — graph visualisation
- Free open-source graph layout tool. Excellent for architecture diagrams.
- Grzegorczyk hierarchy / logic notes
- Free peer-reviewed Stanford Encyclopedia entries on logic. Rigorous.
- Guido van Rossum's blog
- Free writing on Python and programming. Timeless and thoughtful.
- Haskell — learn you a Haskell
- Free excellent introductory Haskell book. Best place to start FP.
- How to contribute to open source
- Free practical guide to making your first open source contribution. Very good.
- HTTP Working Group specs
- Free authoritative HTTP specifications. The real documentation.
- IETF Datatracker
- Free authoritative view of all internet standards in progress.
- Isabelle/HOL
- Free proof assistant with a very readable Isabelle/HOL introduction.
- Khan Academy — Computer Science
- Free courses on algorithms, programming, SQL and web design. Solid start.
- Lean mathlib — documentation
- Free Lean community hub, with tutorials and the mathlib project.
- Lean theorem prover (free)
- Free, open-source proof assistant with excellent docs and a friendly community.
- mathlib4 (Lean)
- Free formalised mathematics library in Lean. Enormous and impressive.
- MDN Web Docs
- The best free reference for web technologies. Authoritative and complete.
- Mermaid diagrams
- Free diagram-as-code for markdown. Perfect for README files.
- MIT 6.001 — SICP (OCW)
- Free MIT course with the full SICP video lectures. Exceptional teaching.
- MIT 6.042J — Mathematics for Computer Science
- Free MIT course on discrete maths for CS. The essentials, well taught.
- Mizar — free proof system
- Free proof system for mathematics with a large free library.
- Nand2Tetris — HDL projects
- Free course projects: build CPU, RAM, assembler, compiler from scratch.
- NumFOCUS — open scientific projects
- Free directory of open-source scientific Python projects. Very useful.
- Open Logic Project
- Free open textbooks on formal logic. Very well written.
- Open Source Guides
- Free guides on how to use, contribute to and maintain open source.
- OpenDSA — data structures and algorithms
- Free textbook and Java/C++ library for data structures and algorithms.
- OpenIntro Statistics (free)
- Free peer-reviewed intro statistics textbook with free R labs.
- OSS Insight
- Free data explorer for open source project history. Very cool.
- Paul's Online Math Notes
- Free complete notes on algebra, calculus, discrete maths and statistics. Huge.
- PlantUML
- Free open-source tool for UML and diagram-as-code. Very useful.
- Probability and Computing (free PDF)
- Mitzenmacher & Upfal's free notes on randomized algorithms. Excellent.
- Proof Assistants Stack Exchange
- Free Q&A on Lean, Coq, Isabelle and formal methods. Great for learning.
- RFC Editor
- The free official repository of all RFCs, including HTTP and internet standards.
- Rich Hickey's blog
- Free writing on Lisp, Clojure and software design. Deep and long.
- SageMath
- Free open-source mathematics software. Play with algebra and number theory.
- Seeing Theory (free)
- Free interactive visualisations of probability and statistics. Superb.
- SICP — full text free (MIT Press)
- Structure and Interpretation of Computer Programs, complete and free. A classic must-read.
- SICP JS edition (free)
- SICP reworked for JavaScript, free online. A modern approach to the same ideas.
- Sindre Sorhus' blog
- Free, high-quality open source developer's blog on tooling and design.
- SMT solvers (free)
- Free open-source theorem prover from Microsoft. Very fast and powerful.
- Software Heritage
- Free archive of all public source code. Remarkable resource.
- Statistical Rethinking (free PDF)
- McElreath's Bayesian course, free PDF. The best stats course out there.
- Statistics Done Wrong (free)
- Free book on statistical mistakes in research. Eye-opening and short.
- Swift — the language
- Free official Swift documentation. Well written and current.
- SymPy — symbolic maths
- Free open-source symbolic mathematics library. Great for learning maths.
- The Odin Project
- Free, project-led full-stack curriculum. Rigorous, no hand-holding.
- Think Bayes (free)
- Downey's free book on Bayesian thinking. Very practical and clear.
- Think Stats (free)
- Downey's free statistics book using Python. Learn stats by coding.
- Tree-sitter — parser generator
- Free open-source incremental parser generator. Modern and fast.
- Trustworthy Online Controlled Experiments
- Kohavi, Tang & Xu's free online experimentation book. Practically useful.
- TypeScript handbook
- Free official TypeScript handbook. The best typed-JS reference.
- W3C specifications
- Free web standards: HTML, CSS, SVG, accessibility. Authoritative.
- WAI — Web Accessibility Initiative
- Free accessibility standards, tutorials and evaluation tools. Must-read.
- web.dev
- Free Google-authored guides on web performance, PWA and modern browser features.
- WebAIM — accessibility articles
- Free clear accessibility guides. Very practical and well written.
- WHATWG HTML standard
- The free living HTML standard. Surprisingly readable and definitive.
CS fundamentals
- Advent of Code
- Annual December coding puzzles. Great for learning a new language.
- Algorithms by Jeff Erickson
- Gorgeous free algorithms textbook. Highly visual and rigorous.
- Berkeley CS186 (databases)
- Free DB internals course: indexing, query optimization, transactions. Gold.
- Big-O complexity cheatsheet
- Complexity of common operations. Quick reference.
- Complexity Zoo
- Fun illustrated catalogue of complexity classes. For the curious.
- CP-Algorithms
- Deep algorithm dive with proofs. Excellent for competitive programming.
- Exercism
- Free mentored practice problems in dozens of languages. Great for hands-on fluency.
- freeCodeCamp
- Free, project-based curriculum with certifications. Good for JS/web.
- Harvard CS50 (free)
- Intro CS course fully free with lectures and problem sets. Great start.
- Interactive linear algebra (Ben Spector)
- Free interactive linear algebra textbook. Outstanding for intuition.
- MIT 6.1810 Operating System Engineering
- Build an OS kernel (xv6) in C. Free lectures + labs. Best OS course.
- MIT OpenCourseWare
- Free, complete university courses (CS, EE, math) with lectures + assignments.
- Operating Systems: Three Easy Pieces
- The best free OS book. Virtualization, concurrency, persistence.
- Project Euler
- Mathematical programming problems. Excellent mental training.
- Stanford CS229 notes
- Andrew Ng's ML course notes — the classic free ML reference.
- The Annotated Turing
- Neil Sloane's annotated history of the Turing machine. Fascinating.
- Theoretical Computer Science SE
- Rigorous Q&A. Great for understanding CS concepts deeply.
- Theory of Computing (Boaz Barak)
- A beautifully modern free TCS textbook. Highly recommended.
- Tim Roughgarden's theory courses
- Free algorithms / optimization / complexity notes. Gold standard rigor.
- Visualgo
- Step-through visualizations of sorting, graphs, B-trees.
- Visualizing Algorithms (Bret Victor)
- Animated algorithm visualizations. Brilliant pedagogy and design.
- xv6 source (MIT)
- The teaching OS source. Small, clean, readable.
Data Engineering
- Apache Airflow documentation
- The free official Airflow docs. Orchestration, DAGs and providers.
- Apache Arrow documentation
- The free columnar format docs. The backbone of modern data systems.
- Apache Flink documentation
- The free Flink docs for stream processing at scale.
- Apache Iceberg documentation
- The free docs for Apache Iceberg, the open table format.
- Apache Parquet documentation
- Free docs for the Parquet columnar format. Useful reference.
- Data Is Plural (free projects)
- Free guided data journalism projects. Excellent for learning by doing.
- Database Internals (Alex Petrov)
- A free deep series on B-trees, LSM-trees, WAL and storage engines. Essential.
- Databricks Engineering blog
- Free deep technical posts on distributed data systems. Excellent.
- dbt documentation (free)
- The free official dbt docs. The standard for data transformation.
- dbt Labs blog (free)
- Free technical blog on analytics engineering. Well written.
- Deequ documentation (free)
- Free open-source data quality constraints library for Spark. Very good.
- Delta Lake documentation (free)
- Free docs for Delta Lake, the open table format. Very good.
- DuckDB documentation (free)
- Free in-process OLAP docs. Excellent for local analytics.
- GitLab engineering handbook (free)
- The best public engineering handbook, including their database design guidance. Free.
- Great Expectations docs (free)
- Free data quality framework docs. Very practical.
- OpenLineage documentation
- Free docs on data lineage standards. Increasingly important.
- Percona blog (free)
- Free deep technical blog on databases and open source. Very strong.
- Polars documentation (free)
- Free Polars docs. Fast DataFrames in Python and Rust.
- Postgres Tips
- Free practical PostgreSQL tips, mostly short and very useful.
- PostgreSQL wiki (community)
- The free community wiki. Lots of hard-won knowledge and recipes.
- Snowflake engineering blog (free)
- Free technical blog on data engineering at scale. Very practical.
- SQL style guide (free)
- The free SQL style guide. Readable SQL is a real team benefit.
- The Art of PostgreSQL (free online)
- A free online book on PostgreSQL internals and practice. Outstanding.
- The Data Engineering Podcast
- Free weekly podcast interviewing data engineers. Very informative.
- The Data Journalism Handbook (free)
- A free book on doing rigorous data journalism. Very well written.
- Vlad Mihalcea's blog
- Free deep blog on database performance, Hibernate and caching. Excellent.
Data Science
- Analysis of variance
- ANOVA, when it is appropriate, and the cases where it is not.
- Apache Hadoop
- HDFS and MapReduce, the system that made big data a thing and is now mostly legacy.
- Apache Spark
- The in-memory successor. Its architecture doc explains why the shuffle design costs what it does.
- Backpropagation
- The chain rule applied to a computation graph, and the historical confusion about it.
- Bias–variance tradeoff
- The central idea in supervised learning, stated once and used everywhere.
- Bloom filter
- Probabilistic set membership. The false-positive maths is short and worth knowing.
- Chi-squared test
- The workhorse categorical test, with the assumptions it actually requires.
- Confidence interval
- What a 95% confidence interval does and does not mean. Read before quoting one.
- Confusion matrix
- The table everything else is derived from. Understand it and F1 becomes trivial.
- Convex optimization
- Why convexity is the property that makes optimisation tractable, and the algorithms it enables.
- Count–min sketch
- Approximate frequency counting in sublinear space. Used in every real analytics system.
- Cross-validation (statistics)
- K-fold and its leaky variants, and the grouped and time-series cases that matter in practice.
- Data lake
- Why the lakehouse pattern emerged, and the consistency problem it solves.
- Data mesh
- The decentralised ownership model, argued carefully by its proponents and here neutrally.
- Data quality
- Dimensions, measurement, and the practical parts of keeping data trustworthy.
- Data warehouse
- The columnar model and the schema evolution story, which drives most modern formats.
- Effect size
- The number that actually matters, as opposed to whether a p-value cleared a threshold.
- Ensemble learning
- Bagging and boosting, and the variance reduction intuition that unites them.
- ETL
- The classic pipeline pattern and where it breaks down at scale.
- Exploratory data analysis
- What EDA is actually for, which is deciding what to model rather than modelling immediately.
- F-score
- Precision, recall and their harmonic mean, and the cases where F1 is the wrong choice.
- Feature engineering
- The highest-leverage part of most tabular problems, and usually where the real work is.
- Feature store
- The infrastructure pattern for keeping training and serving features consistent.
- Foundations of Data Science (free book)
- A free, rigorous statistics text focused on forecasting and time series. Excellent, and complete.
- Gradient
- The mathematical object every optimiser is manipulating, defined properly.
- Gradient boosting
- Why boosting works, and the difference between the sklearn and XGBoost/LightGBM algorithms.
- Gradient descent
- The optimisation algorithm and its variants, from vanilla to adaptive methods.
- HyperLogLog
- Cardinality estimation in a few kilobytes. Redis built it into its core commands.
- Locality-sensitive hashing
- The randomised trick that makes approximate nearest neighbour search sublinear.
- Loss function
- From empirical risk to the actual loss, and why the choice changes what the model learns.
- MapReduce
- The original paper. Still the clearest explanation of the shuffle's cost.
- Matplotlib
- The Python plotting standard. Its gallery is the fastest way to learn how to make a figure readable.
- Maximum likelihood estimation
- The estimation principle behind most classical models, with its assumptions spelled out.
- Nearest neighbor search
- From brute force to HNSW and IVF, and the recall-latency tradeoff at the centre of it.
- NumPy
- The array library everything is built on. Read the C source to understand what is actually fast.
- Overfitting
- The mechanism, the detection, and why validation splits can themselves overfit.
- P-value
- The definition and, more usefully, the extensive list of ways it gets misused.
- pandas
- Dataframes. The user guide explains the block manager, which explains the performance traps.
- Random forest
- The Breiman paper's idea, and what it does and does not fix about a single tree.
- Receiver operating characteristic
- ROC and AUC, the trade-off curve, and when precision-recall is the better view.
- Regularization (mathematics)
- L1 and L2 from the variational view, which explains why L1 produces sparse solutions.
- Resampling (statistics)
- Bootstrap and permutation methods, and why they make almost any statistic computable.
- SciPy
- Scientific computing in Python. The cookbook answers most numerical questions you will have.
- seaborn
- Statistical plotting on top of matplotlib, where the defaults are already sensible.
- Sensitivity and specificity
- The two properties of a classifier that trade off against each other, with the Bayes framing.
- SimHash
- Near-duplicate detection in a few lines. Simple and immediately useful.
- Statistical model
- The definition, and how model selection is actually justified.
- Statistical power
- Why an underpowered study is not a small result, it is no result.
- Stochastic gradient descent
- Why minibatching works, and the momentum and adaptive methods built on it.
- Stream processing
- Event time versus processing time, and the windowing semantics you have to get right.
- The Journal of Statistical Software
- Every issue is free and peer reviewed. The place to find the actual algorithm behind a method.
- Type I and type II errors
- The two ways a test goes wrong, and the power calculation that comes with them.
- Vector database
- What the category actually is, and the index types that make it work.
Databases
- CockroachDB documentation
- Distributed SQL with Raft. Free docs plus a strong consensus blog.
- Cybertec — PostgreSQL blog
- Deep, practical PostgreSQL tuning, internals and news. High signal.
- Database design pitfalls
- Constraints and schema design are the best cheap performance wins.
- Datasette (SQLite as an API)
- Instantly publish SQLite as an API and browsable site. Very cool.
- dbdiagram.io
- Design DB schemas visually with a simple DSL. Free tier is generous.
- dbdocs.io
- Browse and search Postgres/MySQL/SQLite documentation. Handy.
- Django ORM docs
- A great batteries-included ORM with excellent documentation.
- Dolt (version-controlled SQL)
- Git for data. Branch, diff and merge your database tables.
- DuckDB
- In-process OLAP (SQLite for analytics). Amazing for local data work.
- etcd documentation & internals
- The Raft-based KV store behind Kubernetes. Learn from it.
- FoundationDB internals
- Apple's open-source distributed KV database. Excellent engineering docs.
- InfluxData blog
- Time-series storage engines and observability data. Good internals.
- LSM-tree overview (Martin Kleppmann)
- Excellent research blog with database internals papers and posts.
- Materialize blog
- Incremental view maintenance and streaming SQL. Advanced, fascinating.
- MongoDB engineering blog
- Document-model trade-offs, sharding and the WiredTiger engine.
- pganalyze blog
- Postgres performance, monitoring and index tuning with good tooling.
- pgvector
- Vector similarity search in Postgres. Standard for RAG systems now.
- Postgres Professional blog
- More deep Postgres internals: MVCC, storage, query planning.
- PostgreSQL documentation
- The definitive Postgres manual. Massive but the reference of record.
- PostgreSQL EXPLAIN docs
- Read the EXPLAIN and query planning chapters. High leverage.
- PostgreSQL partitioning
- Declarative partitioning, the scalable way to handle big tables.
- Prisma ORM (Node)
- Typed ORM for Node with great docs. Common in TS stacks.
- QuestDB blog
- Time-series internals, performance and columnar storage. Good writing.
- Redis blog
- Redis internals, data structures and the ecosystem. Deep technical posts.
- SQLAlchemy documentation
- The most flexible Python SQL toolkit. Excellent reference docs.
- SQLite documentation
- Beautifully written SQLite docs. Reading these teaches SQL broadly.
- SQLite full-text search (FTS5)
- Full-text search without a separate engine. Often overlooked.
- SQLite: Why Not Git?
- The best single essay on data modeling and versioning. Must-read.
- Timescale blog
- Time-series Postgres, hypertables and analytics at scale.
- Use The Index, Luke
- The best free resource on SQL indexing, plus a free e-book. Essential.
- Vitess documentation
- Horizontal sharding of MySQL. Best-in-class scaling docs.
Dev blogs
- A List Apart
- Long-running publication on web design, content and engineering.
- Adam Johnson (Django)
- Django deep dives, architecture and incremental improvement. Great prose.
- Antoine Pitrou (antoinep.org)
- CPython core dev on performance, the GIL and how Python really works.
- Austin Byers (Fallible / random notes)
- Introspection on engineering management and team effectiveness.
- Brendan Gregg's Blog
- eBPF performance observability, flame graphs, system forensics. Gold.
- Charity Majors (charity.wtf)
- Observability, incident response and engineering culture. Sharp and honest.
- Coding Horror
- Classic blog on the pains and absurdities of software development. Still fun.
- composition.dev
- High-level design patterns for frontend. A great free curriculum.
- Dan Luu
- Developer productivity data, startup realities, systems and career.
- Egor Rogov (pure.blog)
- Rust, systems programming and thoughtful engineering essays.
- Ethan Lee (fluent.rs)
- Systems, performance, and hardware-software co-design essays. Sharp.
- Increment magazine
- Thoughtful long-form articles on software development. Free to read.
- Joel on Software
- Classic essays on software teams, process and leaky abstractions.
- Julia Evans — Wizard Zines
- Absolutely the best learning-in-public blog: git, DNS, TCP, Go profiling.
- Kevin Quirk (kevquirk.com)
- Programming, performance and puzzles. Deep, independent, and fun.
- LWN.net
- The best technical Linux journalism. Kernel internals, weekly.
- man7.org (Michael Kerrisk)
- The Linux man-pages author. Precise, careful, authoritative on syscalls.
- Martin Fowler
- Refactoring, architecture and delivery. His bliki is endlessly useful.
- Martin Fowler on bliki
- Short opinionated pieces on architecture and delivery topics.
- Matteo Collina (thisdoesnot.dev)
- Node.js performance, undici, and building fast services. Practical.
- Mike Solovyov (missolney.com)
- Software engineering, management and craft. Highly thoughtful essays.
- Mirek Nakon
- SRE and performance engineering. Data-driven approach to operations.
- Nadia Eghbal
- Technical leadership and writing about engineering organizations. Thoughtful.
- Patrick Loeber batchnorm
- Python and performance explainers. Clear teaching style.
- Rachel by the Bay
- Security, infra and a very human voice. War stories worth reading.
- Simon Willison's Weblog
- AI plus tools, TILs, and long-running experiments. Read it daily.
- Steve Yegge (be excellent to each other)
- Career essays, AI coding agents, and platform strategy. Provocative.
- The Pragmatic Engineer
- Career growth, engineering management and technical strategy. Practical.
- The Stack Overflow Blog
- Surveys, data, and engineering practice posts from a respected voice.
- Will Larson (larson.tech)
- Engineering leadership, staff-plus growth, and org design. Strong.
- Xe Iaso
- Linux, eBPF, security, and the culture of systems programming. Great.
- Zabole (destroyingwhiteboxes.com)
- Testing philosophy and the real cost of white-box tests. Sharp.
DevOps / Infra
- Alertmanager
- Alert grouping, inhibition and routing. Where on-call pain is actually solved.
- Ansible documentation
- Agentless configuration management. Still excellent for fleet ops.
- Ansible Documentation
- Modules, playbooks, collections and the idempotence model that makes automation safe to re-run.
- Ansible Galaxy
- Thousands of free roles and collections. Where most real Ansible code comes from.
- Apache Kafka
- The event log everything from CDC to streaming pipelines is built on. Read the design section.
- Apache Kafka documentation
- Topics, partitions and exactly-once. The reference of record.
- Apache ZooKeeper
- Coordination primitives, and a useful read for understanding what newer systems are replacing.
- Arch Linux
- Rolling release, minimal base, and documentation as a first-class feature. Read the wiki first.
- Argo CD
- GitOps continuous delivery for Kubernetes. Declarative, and the sync model is worth understanding regardless of tool.
- Argo Project
- Argo CD and Workflows: pull-request based CD for Kubernetes. Very handy.
- Argo Workflows
- Container-native workflow engine for Kubernetes. The right tool for data and batch pipelines on the platform.
- Backstage
- The developer portal framework. Why a service catalog is the first thing to build at scale.
- Buf — protobuf tooling
- The modern way to manage protobuf schemas. Adopt early.
- Caddy documentation
- Modern web server with automatic HTTPS by default. Nice docs.
- Calico
- The other major Kubernetes network plugin, and the most complete network policy implementation.
- Carvel
- A different take on packaging for Kubernetes: ytt, kbld, imgpkg and kapp, without a template language.
- Ceph documentation
- The object store and block device most self-hosted storage is built on.
- Chef
- Infrastructure automation with a Ruby DSL. Less common now, still widely deployed.
- ClickHouse documentation
- Columnar analytical database. The best free docs in the industry for query optimisation.
- CNCF
- Home of Kubernetes and Prometheus. Landscape and case studies.
- CNCF case studies
- How organisations actually adopted this stack, including the parts that went badly.
- CNCF landscape
- Every CNCF project mapped by category and maturity. The best single index of the ecosystem.
- Consul
- Service discovery, health checks and distributed key-value, from HashiCorp.
- Crossplane
- Cloud infrastructure as a Kubernetes API. Composing provider resources into platform APIs.
- Debian
- The stable server distribution. The oldest Linux distribution still shipping.
- Debian manuals
- The reference manuals, including the Administrator's Handbook. Free, complete, and the actual standard.
- Determinate Systems Nix blog
- High-quality Nix guides and best practices. Great for getting unstuck.
- DevOps Exercises
- Hands-on exercises across Linux, networking, security and CI. Free and well structured.
- DigitalOcean community tutorials
- Very detailed step-by-step guides for self-hosting stacks. The most consistently current of the tutorial sites.
- Docker Compose specification
- The compose file format, properly specified. How multi-container local and production stacks are actually defined.
- Docker documentation
- Dockerfile best practices, Compose and buildx. The basics still matter.
- Elastic observability
- Logs, metrics and traces in one place. Free tier, and the strongest log search.
- Envoy
- The L7 proxy that became the service mesh default. Worth reading the architecture docs for the data-plane model.
- Envoy Proxy documentation
- Service mesh proxy. Advanced, but the docs are excellent.
- etcd
- The strongly consistent key-value store everything else in the Kubernetes ecosystem depends on.
- External Secrets Operator
- Syncs secrets from any external provider into Kubernetes. The vendor-neutral option.
- Falco
- Runtime security for Kubernetes from eBPF syscall data. Unexpected syscall use is the actual signal.
- Flux
- The CNCF GitOps alternative to Argo CD, and the GitOps Toolkit underneath it.
- Fly.io docs and guides
- Deploy close to users with great guides. Good mental model for edge.
- Gatekeeper
- Admission control for Kubernetes, using OPA. How you stop a bad manifest reaching the cluster.
- GitHub Actions documentation
- CI/CD that lives with your code. Good docs, huge ecosystem.
- GitLab CI documentation
- A complete CI reference built into the repository, and the model for pipeline-as-code.
- Grafana
- Dashboards and visualization, and the de facto front end for everything above.
- Grafana Loki
- Log aggregation that indexes labels rather than content. Cheap enough to keep everything.
- Grafana Tempo
- Distributed tracing backend, and the reference for how trace volume is controlled.
- gRPC core concepts
- Core concepts and patterns for gRPC across languages.
- HAProxy
- Layer 4 and 7 load balancing with a very expressive configuration language.
- Harbor
- A private registry with signing, scanning and replication. The default choice for a real container registry.
- HashiCorp Terraform
- Infrastructure as code, and the provider ecosystem that made it the default.
- HashiCorp Vault
- Secrets management with dynamic credentials and encryption as a service.
- Helm — the Kubernetes package manager
- Charts, releases and templating. Still the most common way to package Kubernetes workloads.
- Helm documentation
- The K8s package manager. Learn it for chart management.
- HowToForge
- Long-running tutorials for actually installing and configuring self-hosted software. Dated in places, invaluable in others.
- InfluxDB documentation
- Time-series storage and the query language, and where time-series databases stop making sense.
- Jenkins Pipeline documentation
- The Pipeline book, and the clearest explanation of a Groovy DSL for CI that exists.
- k9s
- Terminal UI for Kubernetes. Once you use it you never go back.
- KICS — IaC scanning
- Infrastructure-as-code scanning across Terraform, Dockerfiles, Kubernetes and more.
- Killer.sh
- Realistic Kubernetes scenarios in a browser terminal. Free tier, and the closest thing to a rehearsal.
- kind (Kubernetes in Docker)
- Run a real Kubernetes cluster locally in Docker. Great for testing.
- kube-bench
- Runs the CIS benchmark against a cluster. Free and the fastest hardening win available.
- kube-linter
- Static checks for Kubernetes manifests, run in CI before they ever reach a cluster.
- Kubernetes concepts
- The part that explains *why* the system behaves as it does, rather than how to type the commands.
- Kubernetes documentation
- The reference: concepts, tasks, reference, tutorials.
- Kubernetes the Hard Way
- Builds a cluster by hand with no cloud provider. The best way to understand what actually runs where.
- Kustomize
- The alternative to Helm: overlay patches instead of templates. No chart lock-in.
- Kyverno
- Policy and mutation for Kubernetes without a separate language. Usually the lower-friction choice.
- Learn Kubernetes (Kelsey Hightower)
- The famous hands-on Kubernetes labs. Excellent for learning properly.
- Longhorn
- Replicated block storage on Kubernetes, with snapshots. Simpler than Ceph for smaller clusters.
- Mise — dev tool manager
- Manage language runtimes and CLI tools with one config. Modern asdf.
- MongoDB documentation
- The document database reference, including the indexing and aggregation framework.
- Netdata
- Real-time per-metric monitoring with almost no configuration. The fastest way to see a problem.
- Netshoot
- One container with every network debugging tool preinstalled. Saves an afternoon per incident.
- NGINX documentation
- The reverse proxy most of the internet runs on, plus the admin guide that still matters.
- Nix package manager & docs
- Reproducible builds and dev environments. Deep ecosystem worth learning.
- NixOS
- A whole OS built around declarative, reproducible configuration.
- NixOS Learn
- Free structured courses on Nix and NixOS, from first principles to flakes.
- OPA source (GitHub)
- The full source, with a well-written documentation set on the Rego language.
- Open Policy Agent
- General-purpose policy engine. A small, well-specified language that outlives most of its use cases.
- OpenGitOps specification
- GitOps principles and tooling. A clean mental model for CD.
- OpenSearch
- The community fork of Elasticsearch. Search and log analytics, self-hosted.
- opensource.com
- The Red Hat publication: how open source is actually used, and the case studies behind it.
- OpenTelemetry
- Vendor-neutral observability: traces, metrics, logs. Learn the standard.
- OpenTelemetry specification
- The actual specification, in the open. The clearest way to know what your instrumentation guarantees.
- Packer
- Machine images built from code, the same way Terraform does everything else.
- Play with Docker
- Free browser-based Docker and Kubernetes sandboxes. Nothing to install.
- Postmortem culture (Google SRE ch.15)
- How to run blameless postmortems. Free and practical.
- pre-commit framework
- A fast, multi-language pre-commit hook manager. Simple quality gate.
- Prometheus
- The metrics system that defined the monitoring stack. Understanding it means understanding most of the ecosystem.
- Prometheus documentation
- Metrics and alerting. The de-facto monitoring standard.
- Proxmox VE
- Free hypervisor for homelabs and self-hosting. Worth knowing.
- Pulumi
- Infrastructure as code in real programming languages, with the escape hatch Terraform lacks.
- Pulumi documentation
- Infrastructure as code in TypeScript, Go or Python. Escape from HCL.
- Puppet
- Declarative configuration management, and the DSL built around reporting drift.
- RabbitMQ
- AMQP messaging with an excellent tutorial series, still the clearest introduction to queues.
- Redis documentation
- In-memory data structures, and an honest look at when a cache is the wrong tool.
- Renovate (dependency updates)
- Automated dependency updates. Set it up; stop manual chores.
- Rook
- Ceph on Kubernetes. Storage is the hardest part of self-hosting and this automates it.
- Sealed Secrets
- Kubernetes Secrets encrypted so they can be committed. The GitOps answer to secret sprawl.
- Server Fault
- Question-and-answer for sysadmins. The archive of hard-won answers is the real value.
- Skaffold
- Continuous delivery for Kubernetes. Local dev loop tool.
- SOPS — Secrets Operator for Encryption
- Encrypts values inside YAML, JSON and env files so secrets live in git safely. Simple and widely used.
- Tailscale
- WireGuard-based mesh networking with a hosted control plane. The easiest flat network you will set up.
- Tailscale knowledge base
- Zero-config mesh VPN. The KB is superb.
- Tekton
- CI/CD primitives as Kubernetes custom resources. How far the ‘pipelines as code’ idea goes.
- Temporal
- Durable workflow execution. The clearest answer to ‘what if the process crashes halfway through’.
- Temporal source (GitHub)
- The Go server implementation, which is also good Go code to read.
- Terraform docs and tutorials
- IaC reference plus free tutorials. The standard for cloud provisioning.
- Terraform Registry
- Reusable infrastructure modules from the community.
- Thanos
- Long-term Prometheus storage and global query across clusters.
- The Illustrated HTTP
- A friendly illustrated reference to the HTTP protocol. Handy.
- Tilt (dev loop)
- A nicer local dev loop for multi-service Kubernetes apps.
- Traefik
- The modern reverse proxy: automatic service discovery and certificates from labels.
- Traefik documentation
- Reverse proxy and ingress with dynamic config. Well documented.
- Trivy
- Vulnerability and misconfiguration scanning for images, repos and IaC. Free, fast, everywhere.
- Ubuntu Server documentation
- The default cloud server distribution, with clear and current documentation.
- Vagrant
- Reproducible local development environments. Still the cleanest answer to ‘works on my machine’.
- WireGuard protocol
- A simple, fast, modern VPN protocol. Small and readable spec.
- Wireshark documentation
- The definitive network protocol analyzer and its docs. Learn to read packets.
- Woodpecker CI
- A lightweight open-source CI alternative. Clean and small.
Efficiency & Algorithms
- Algorithmic paradigm
- Divide and conquer, greedy, DP and the rest, with when each applies.
- Amortized analysis
- Why a dynamic array append is O(1) amortized, and what that buys you in practice.
- Big O notation
- What the notation does and does not say, including the limits of comparing it casually.
- Cache-oblivious algorithm
- Algorithms that do not know the cache geometry. The most important idea in modern algorithm design.
- Copy-on-write
- COW in filesystems, VMs and strings. Cheap until the write happens.
- Data structure
- The core structures, with the complexity table you will keep referring to.
- Dynamic dispatch
- vtables, devirtualisation, and what makes a method call slow.
- Dynamic programming
- Memoisation and tabulation, and how to recognise when it is the right tool.
- Greedy algorithm
- The exchange argument that justifies greedy, and the cases where it fails.
- JavaScript Algorithms
- Algorithms and data structures in JS, each with a linked explanation. The best explanations in the set.
- Non-blocking algorithm
- Lock-free and wait-free algorithms, and the progress guarantees that distinguish them.
- NP-hardness
- What it means, why it matters, and the practical difference between NP-hard and just slow.
- Python Package Index
- The Python package index. Useful for finding implementations before writing your own.
- Reference counting
- The GC you pay for whether you want it or not, and its cycle problem.
- Space complexity
- In-place versus out-of-place, and why space is often the real constraint.
- Tail call
- Proper tail calls and trampolines, and the practical effect on stack depth.
- TheAlgorithms — C++
- Well-documented algorithms in readable C++. Useful both as reference and as a reading library.
- TheAlgorithms — Go
- Go implementations, short enough to read in one sitting.
- TheAlgorithms — Python
- The same in Python, and the clearest way to check whether you actually understand an algorithm.
- TheAlgorithms — Rust
- Idiomatic Rust, with unsafe blocks clearly marked where the algorithm requires them.
- Time complexity
- The formal definition, the common classes, and the cases where the notation misleads.
- Waste collection (garbage collection)
- Every GC design: mark-sweep, copying, generational, and the trade-offs between them.
- Write barrier
- How a generational GC stays fast, and what the barrier actually records.
Flutter
- BLoC pattern tutorial (Reso Coder)
- A classic deep tutorial on BLoC for Flutter, building a full app.
- build_runner
- The code-gen runner behind freezed and json_serializable. Learn once.
- Dart codelabs
- Hands-on Dart codelabs, including a complete Flutter app.
- Dart language tour
- The official Dart language tour. Read it if you are new to Dart.
- DartPad (in-browser playground)
- Run Dart and Flutter instantly in the browser. Great for experiments.
- Didac R. — Flutter deep dives
- In-depth Flutter internals: rendering, layout, state, performance.
- Dio HTTP client
- Interceptors, cancel tokens, retry, form data. The capable client.
- drift database
- Strongly-typed SQLite with reactive queries. Great for local-first apps.
- Firebase for Flutter
- Auth, Firestore, Storage. The classic BaaS choice.
- Flame game engine
- 2D game engine for Flutter. A fun way to learn real-time loops.
- Flutter accessibility
- Semantics and screen readers. Make apps accessible by default.
- Flutter add-to-app
- Embed Flutter in existing Android/iOS apps. The full integration matrix.
- Flutter API reference
- Every class, widget and API. The real reference to bookmark.
- Flutter architectural overview
- How Flutter draws pixels: widgets → elements → render objects → raster.
- Flutter community hub
- Official Discord, subreddit and groups. Where to ask questions.
- Flutter cookbook
- Task recipes: forms, images, HTTP, lists, animation, accessibility.
- Flutter documentation
- The main docs hub: widgets, platform channels, accessibility, testing.
- Flutter integration tests
- End-to-end tests running on real devices and emulators.
- Flutter isolates
- Offload heavy work off the UI thread in Dart. Key to avoiding jank.
- Flutter localization
- Real internationalization: dates, numbers, plurals, RTL.
- Flutter official blog (Medium)
- Feature deep dives, samples and announcements from the Flutter team.
- Flutter performance (DevTools, profiling)
- How to profile: DevTools, timeline, shader compilation, frame charts.
- Flutter performance best practices
- Build fast: const widgets, lists, images, rendering. Essential.
- Flutter platform channels
- Talk to native Android/iOS from Dart. Essential for native interop.
- Flutter release notes / what's new
- What changed in each release. Good for staying current.
- Flutter Rust Bridge
- Run Rust inside Flutter for performance-critical work. Advanced but powerful.
- Flutter samples repository
- Official samples: implicit animations, platform channels, add-to-app.
- Flutter web platform integration
- Web and desktop capabilities, and where the platform gaps still are.
- Flutter Weekly newsletter
- Weekly curated Flutter news, packages and articles. Great digest.
- Flutter widget testing
- Finders, pumps and matchers. The practical guide to widget tests.
- Flutter YouTube (official)
- Official talks, codelabs and the monthly 'What's new' stream.
- flutter_bloc / bloc
- Event-driven state management. The most battle-tested option.
- flutter.ink (Bruno's blog)
- Fun, practical Flutter tips and experiments. Good for staying current.
- freezed (code generation)
- Union types, data classes and value equality for models.
- go_router (navigation)
- Declarative, deep-link friendly routing. The default choice now.
- golden_toolkit (golden tests)
- Build flexible golden image tests for your widgets.
- json_serializable
- Generated JSON serialization from your models. Pair with freezed.
- mocktail (mocking for tests)
- Lightweight mocks without codegen. The go-to for Flutter tests.
- pub.dev — packages
- The Dart/Flutter package registry. Check likes and pub points for maturity.
- rFlutter — a book on Flutter architecture
- Free online book on structuring large Flutter apps: MVVM, DI, state.
- Rive (interactive animation)
- State-machine driven animations exported to Flutter and other runtimes.
- riverpod (state management)
- Modern, testable, compile-safe state management. Excellent docs.
- Sentry for Flutter
- Crash reporting and performance monitoring for Flutter apps.
- Shorebird (code push)
- Push Dart code changes without a full store release. A game-changer.
- Supabase for Flutter
- Open-source BaaS wired cleanly to Flutter. Great for fast MVPs.
- Very Good Ventures engineering blog
- Top Flutter/Dart consultancy: state, testing, architecture. Excellent.
- very_good_analysis lint set
- Opinionated lint rules. Turn them on early and save pain later.
Formal Methods
- Abstract interpretation
- Sound over-approximations of program behaviour. The theory behind most static analysers.
- Alloy Analyzer (free)
- A free relational model finder. Excellent for protocol and data modelling.
- CBMC bounded model checker (free)
- A free open-source bounded model checker for C and C++. Very useful.
- Compositionality
- Category theory, which is where compositionality as a proof technique comes from. Advanced but load-bearing.
- Dafny
- Verification built into the language, with the specification and the code in one file.
- Dafny — verification language
- A free language with built-in verification. Much easier to learn than Coq.
- Frama-C — C verification (free)
- A free open-source toolset for verifying C code with weakest preconditions.
- Hoare logic
- Preconditions and postconditions. The oldest practical formalism still taught.
- Model checking
- Exhaustive state-space verification. The strongest correctness argument you can make about software.
- SMT-LIB benchmarks
- The free standard benchmark suite for SMT solvers. Useful reference.
- SPIN
- The model checker used to find the Java memory model bug, and still the clearest tool for concurrency bugs.
- SPIN model checker (free)
- The free original model checker for concurrent systems. Classic.
- Static analysis
- Finding bugs without running the code, and the trade-off with false positives.
- Theorem prover
- Automated proof assistants, and why some of them now verify real kernels.
- TLA+ — Lamport's specification language
- The free official TLA+ home. Learn to specify concurrent and distributed systems.
- TLA+ Toolbox (free download)
- The free TLA+ model checker and editor. Powerful and worth learning.
- Type theory
- Types as propositions, and why dependent types found a real audience in systems languages.
- UPPAAL (free)
- A free model checker for timed systems. Used in industry.
- Why3
- A multi-prover verification platform with a well-chosen logic for the discipline.
- Why3 — verification platform
- A free verification platform with many provers. Used by Airbus.
- λ-calculus
- The minimal model of computation, and the basis of functional language type systems.
Go
- A Tour of Go
- The official interactive tutorial. Do it once, start to finish.
- Context in Go (official blog)
- Why context.Context exists and how to use it correctly.
- Delve debugger
- The Go debugger with DAP support for editors. The go-to debug tool.
- Effective Go
- The idiomatic-Go essay. Short and essential.
- Go Blog
- Release notes, design rationale, proposals, and the annual survey.
- Go by Example
- Annotated example code. Best way to get quick syntax fluency.
- Go Code Review Comments
- The de-facto style + design review checklist.
- Go error handling guide
- How the Go team thinks about errors. Great design discussion.
- Go fuzzing tutorial
- Native Go fuzzing. Practical way to harden parsers.
- Go generics tutorial
- The official generics tutorial, with type parameters explained.
- Go Lab (Delve, pprof, stats)
- Jonathan Amsterdam's deep dives on Go tooling, tracing and debugging.
- Go memory model
- The rules for memory visibility across goroutines. Read once, understand forever.
- Go pipelines (concurrency)
- The practical pipelines pattern with a clear walkthrough.
- Go profiling docs (pprof)
- Go's built-in profiling endpoint. Learn before you optimize.
- Go Proverbs
- Write straight code; clear beats clever; don't fear small interfaces.
- Go talks conference
- Official conference talks, all with slides and video.
- Go Time (Changelog podcast)
- The best regular Go podcast. Deep interviews with the core team.
- Go Weekly newsletter
- Weekly curated Go links. Low noise, high signal.
- golang.org/x/sync/errgroup
- The idiomatic bounded-parallelism tool. Read the examples.
- pkg.go.dev
- The canonical module and package documentation browser.
- Structured logging with log/slog
- The stdlib structured logger; design article explains the choices.
- The Go Language Specification
- The actual language contract. Reference, not bedtime reading.
- The Go Programming Language
- Home base: docs, blog, releases, package index.
- The official Go Wiki
- Community wiki: best practices, error handling, concurrency, FAQ.
Go blogs
- Brad Fitzpatrick
- Go + HTTP, long-running services, and thoughtful engineering takes.
- Cloudflare Blog — tag Go
- Heavy real-world Go at massive scale. Consistently excellent.
- Dave Cheney — High Quality Software
- One of the best Go blogs. GC, defer, debugging, pitfalls.
- Deliveroo Engineering
- Ruby→Go migrations, Kubernetes, resilience, mobile infra.
- Discord Engineering Blog
- Rust and Go at extreme concurrency. Deep systems posts.
- Dustin Ingram (di.fm)
- Podcast and blog on distributed systems, mostly written in Go.
- Filippo Valsorda
- Go crypto, TLS, certificate internals, module supply-chain security.
- Grab Engineering Blog
- How Grab rebuilds systems in Go, plus payments and data infra.
- Ian Lance Taylor (morsedb)
- GC, allocation and runtime internals by a Go maintainer. Deep.
- Monzo Technology Blog
- How a bank runs on Go and Kubernetes. Honest and detailed.
- Rob Pike's Blog
- Go's co-creator. Lessons from 40+ years of systems work.
- Shopify Engineering
- Ruby→Go rewrite of the tax engine, plus perf war stories.
- Tailscale blog (Go networking)
- Go + networking done well: netstack, tsnet, DERP. Deep but readable.
- Zalando Engineering Blog
- PostgreSQL at scale, Go microservices, JVM lessons. Great archive.
Go frameworks
- air — live reload
- Live reload for Go web dev. Big QoL win for the inner loop.
- Atlas — schema migrations
- Declarative migrations for SQL databases. Works with ent or plain SQL.
- Bubbletea (TUI framework)
- Elm-architecture TUI framework behind Charm's tools. Worth learning.
- Buf Schema Registry
- Lint, break and push protobuf schemas. The modern protoc setup.
- Buffalo
- Classic Go web framework with generators, migrations, job queue.
- Bun ORM
- Modern composable ORM with good PostgreSQL-first ergonomics.
- chi — lightweight router
- net/http-native router used by countless APIs. Tiny and composable.
- Cobra + Viper (CLI apps)
- The most popular CLI framework. Viper for config. Used by k9s, hugo.
- CockroachDB Pebble (LSM in Go)
- A clean LSM key-value store in Go. Great for storage internals.
- ConnectRPC for Go
- Modern protobuf-over-HTTP RPC. Simpler than gRPC, browser friendly.
- CUE (configuration language)
- Google's language for defining data & constraints. Config validation.
- Dagger (CI/CD in Go)
- CI/CD pipelines as Go code with a deterministic engine. Very cool.
- Echo
- Minimal, extensible, fast Go web framework.
- ent — entity framework
- Graph-based schema/ORM for Go; code generation, no reflection.
- Fiber
- Express-inspired API on fasthttp. Very fast, opinionated.
- franz-go (Kafka client)
- The Kafka client most performance-minded Go teams use.
- fzf — fuzzy finder
- The fuzzy finder that broke into every shell. Written in Go.
- Gin
- The most popular full-featured Go web framework. Huge ecosystem.
- Gitea
- Lightweight self-hosted Git service in Go. A solid Forgejo alternative.
- Glow — markdown pager
- A clean markdown pager in Go. Pleasant for reading docs.
- go-kit
- Deliberately minimal toolkit: transport, logging, metrics, tracing.
- go-micro
- Plugin-based microservice framework. Long-running, very active.
- go-zero (microservices)
- Kitex + goctl: batteries-included microservice framework.
- go.uber.org/mock (gomock)
- The maintained fork of gomock. Standard for interface mocks.
- gofumpt
- Stricter gofmt. The formatter most Go teams actually use.
- golangci-lint
- The de-facto linter aggregator for Go (30+ linters in one run).
- gopls language server
- The official Go language server powering editor intelligence.
- goreleaser
- Automate Go release binaries, Docker images, and multi-arch builds.
- GORM
- The most popular Go ORM. Great migrations, plugins, associations.
- grpc-gateway
- Expose gRPC services as REST/JSON with transcoding.
- koanf configuration
- Lightweight, pluggable configuration management for Go apps.
- Kong CLI parser
- Modern minimal struct-tag CLI parser. Great DX for Go CLIs.
- Kratos (microservices)
- Bilibili-origin microservices framework with proto-first clean layout.
- Kubeshark (Go, eBPF)
- Service-mesh observability built on eBPF. Open-source and instructive.
- Litestream
- Continuous SQLite replication to S3. Amazing for small/edge apps.
- mockery
- Generates testify mocks from interfaces. Common in Go test suites.
- NATS + Go event patterns
- NATS docs are among the best messaging docs on the web.
- NATS Go client
- Official Go client for NATS, a lean messaging system.
- Ogen (OpenAPI codegen)
- OpenAPI v3 generator with zero reflection; very fast generated servers.
- PocketBase
- Single-file Go backend: auth, DB, realtime, admin UI. Great for MVPs.
- protobuf.dev
- Official Protobuf docs and cross-language programming guides.
- restic — encrypted backups
- Fast, secure, deduplicated backups written in Go.
- sqlc — generate Go from SQL
- Write SQL, get type-safe Go. The sweet spot between raw SQL and ORM.
- staticcheck
- The most thoughtful static analyzer for Go. Run it in CI.
- Taskfile (Task)
- A Make alternative with better ergonomics, YAML, and includes.
- Templ (typed HTML templates)
- Type-safe, compile-checked HTML templates with great DX.
- testcontainers-go
- Spin up Postgres/Redis/etc. in Docker for integration tests.
- testify
- The ubiquitous assertion/mock/suite library for Go tests.
- Watermill (event-driven)
- Library for building event-driven apps: pub/sub, queues, streaming.
- WebAssembly in Go
- Compiling Go to the browser with WASM. Official how-to.
- zap (Uber's logger)
- Structured, fast, battle-tested logger with excellent docs.
- zerolog
- The fastest structured logger for Go. Pair with slog or instead of it.
Kotlin
- Arrow (functional programming)
- Functional abstractions: Either, Option, coroutine extensions. Deep toolkit.
- Compose Multiplatform
- Share one UI across desktop, web, iOS and Android from Kotlin.
- Compose Multiplatform tutorials
- Step-by-step CMP tutorials for desktop, web and mobile targets.
- Detekt (static analysis)
- Configurable static analysis and complexity checks for Kotlin.
- Exposed (SQL framework)
- JetBrains' Kotlin SQL framework and ORM. Type-safe DSL.
- JetBrains YouTube
- Broader JetBrains content: Ktor, Compose, IntelliJ, language design.
- Koin (dependency injection)
- Pragmatic, lightweight DI for Kotlin, including Compose.
- Kotlin blog (official)
- Compiler releases and language updates, including the K2 rollout.
- Kotlin coding conventions
- The official style guide. Wire ktlint with these rules.
- Kotlin community (forums, Slack)
- Forums, Slack and events. The place to get Kotlin help.
- Kotlin coroutines guide
- Structured concurrency from first principles. The best coroutine docs.
- Kotlin Design Proposals
- Kotlin Enhancement Proposals: the design process made public.
- Kotlin Discussions (YouTube)
- Community talks on Kotlin in production. Real-world experience.
- Kotlin documentation (new site)
- The restructured Kotlin docs. Much better than the old ones.
- Kotlin DSL (build scripts)
- Type-safe Gradle scripts in Kotlin. Learn build logic properly.
- Kotlin evolution principles
- How the language evolves and why it breaks things. Essential context.
- Kotlin Kover (code coverage)
- JVM and native code coverage from JetBrains. Great for KMP.
- Kotlin Multiplatform (JetBrains)
- Why and how to share Kotlin across platforms. Reference docs and case studies.
- Kotlin official site
- Home base for docs, blog, compiler and roadmap.
- Kotlin source on GitHub
- The compiler source (K1 and K2). Great for compiler internals learning.
- Kotlin YouTube (official)
- KotlinConf talks, K2 deep dives and Multiplatform demos.
- Kotlin/Native and Multiplatform
- Compiling Kotlin to native binaries, and the multiplatform model.
- kotlinx-atomicfu
- Multiplatform atomics and locks for Kotlin. Useful for concurrency.
- kotlinx-datetime
- Multiplatform date and time API, replacing java.time on other platforms.
- kotlinx.coroutines
- Flows, channels, structured concurrency. The async workhorse.
- kotlinx.serialization
- The official multiplatform JSON/protobuf library with a compiler plugin.
- ktlint
- The standard Kotlin linter and formatter. Enforce it in CI.
- Ktor (Kotlin server framework)
- JetBrains' async web framework for server, JVM, Android and native.
- Ktor documentation
- JetBrains Kotlin server framework: routing, auth, serialization, testing.
- Moshi (JSON)
- Fast reflective/codegen JSON parsing from Square. Kotlin-friendly.
Mathematics
- Abstract Algebra: Theory and Applications (free)
- A free complete abstract algebra textbook with exercises and solutions.
- An Introduction to Statistical Learning (free)
- The free official site for ISLR. A classic intro ML/stats textbook.
- Analysis I (Terence Tao, free)
- A free rigorous intro to real analysis. Plus Tao's Analysis II and measure theory.
- Cut-the-Knot (free)
- Free interactive maths applets and essays. Old-school and excellent.
- Fedor Petrov's blog
- Free blog on combinatorics, algorithms and open problems. Very strong.
- Mathematica Stack Exchange (free)
- Free Q&A for CAS systems. Very helpful for Mathematica/SymPy.
- MathWorld (Wolfram, free)
- The best free maths encyclopedia. Look up any theorem, constant or identity.
- MIT 18.01 — Single Variable Calculus
- A free MIT calculus course with full video lectures. Excellent.
- MIT 18.02 — Multivariable Calculus
- A free MIT multivariable calculus course with videos. Rigorous.
- MIT 18.03 — Differential Equations
- A free MIT differential equations course with video lectures.
- MIT 18.100 — Real Analysis
- A free MIT real analysis course. Rigorous, with good problem sets.
- nLab — reference on category theory
- A free collaborative wiki on category theory, homotopy and higher algebra.
- SymPy documentation (free)
- The free SymPy docs. Symbolic maths in Python, ideal for learning.
- Terence Tao's blog
- Free writing on analysis, number theory and research maths. Very deep.
- The Book of Proof (Hammack, free)
- A free, excellent book on mathematical proof. The best place to start.
- Topology Without Tears (free)
- A free point-set topology textbook. Surprisingly gentle and rigorous.
- Wolfram Demonstrations Project
- Free interactive maths visualisations. Brilliant for intuition.
Performance
- Amdahl's law and Little's law
- Two laws every performance-minded engineer should know cold.
- BPF Performance Tools (book site)
- The companion site for his BPF observability book, with 100+ tools and errata.
- Brendan Gregg's home
- The master of system performance, flame graphs and eBPF. Read everything.
- eBPF tools (BCC)
- BPF Compiler Collection. Practically required for Linux perf work.
- eBPF.io primer
- A friendly official intro to eBPF. Great entry point for Linux perf.
- Flame Graphs (original article)
- The original flame graph article. Read it once and it clicks forever.
- High Performance Browser Networking
- Free online book on network performance, latency, TLS and the web stack. Gold.
- Jepsen analyses (distributedsystems.study)
- Real-world consistency testing of databases. Eye-opening research.
- nosnoop (LD_PRELOAD debugger)
- Find memory and CPU issues in unmodified binaries. Great for production.
- perf.wiki.kernel.org
- The community wiki for Linux perf, with practical profiling recipes.
- SQLite tuning (pragma docs)
- Pragmas for tuning SQLite performance, durability and memory.
Rust
- Amos on Gitpod / Rust streams
- The Rust org on GitHub: sub-repos worth skimming (rustc, cargo, rust-analyzer).
- error handling with anyhow/thiserror
- The two crates you'll use for error handling in almost every Rust project.
- Idiomatic Rust (lints clippy)
- Clippy lints describe what idiomatic Rust looks like. Read as a style guide.
- Inside Rust blog
- Deep articles about the compiler internals: rustc, MIR, codegen.
- Learning Rust (Jim Blandy)
- See the official search across all Rust docs, RFCs and code.
- Rust API Guidelines
- How to design pleasant, idiomatic Rust APIs. For library authors.
- Rust async book (Tokio)
- Learn async Rust properly instead of cargo-culting it.
- Rust Blog (official)
- Release posts, dev-notes, initiative updates, annual surveys.
- Rust by Example
- Learn Rust from annotated runnable examples. Great complement.
- Rust CLI Apps book (free)
- Free book on building real, polished Rust command-line tools.
- Rust community hub
- Forums, Discord, IRC, and the RFC repository in one place.
- Rust Compiler Dev Guide
- For contributors: how rustc works, from AST to codegen.
- Rust Compiler Errors (a friendly index)
- Every compiler error has a documented explanation. Superb learning aid.
- Rust Design Patterns
- Applied patterns: errors, iterators, smart pointers, concurrency.
- Rust for Rustaceans (free online)
- Mid-level Rust book, free to read online. Great follow-up to The Book.
- Rust Performance Book
- Benchmarking, profiling and optimization in Rust. Practical and current.
- Rust RFCs
- Read RFCs to understand why Rust is shaped the way it is.
- Rust Users Forum
- The main help forum. Search first; answers are thorough.
- Rustacean Station (podcast)
- The weekly Rust podcast: interviews, learning, ecosystem news.
- Rustlings (exercises)
- Compiler-driven exercises. THE way to build Rust muscle memory.
- Simon Willison on Rust
- Practical notes from rewriting real tools in Rust. Good 'why' material.
- The Rust Edition Guide
- What changed in editions 2018/2021/2024. Matters for real code.
- The Rust Programming Language (The Book)
- The definitive free Rust book. Start here and read most of it.
- The Rust Reference
- The precise language spec. Unmatched detail reference.
- The Rustonomicon
- Unsafe Rust, FFI and UB. Deep, free, genuinely fascinating.
- This Week in Rust
- The weekly community digest. Best way to track the ecosystem.
Rust ecosystem
- Actix Web
- Extremely performant web framework, batteries included.
- Anchor (Solana Rust)
- The Rust framework for Solana programs. Clean smart-contract code.
- axum + tower middleware
- Tower is the middleware stack behind axum. Learn it for reusable services.
- Axum web framework
- Tower-based, extractor-driven web framework. Ergonomic and well documented.
- bat — cat with highlighting
- Clean, idiomatic Rust. Great starter project to read end to end.
- Bevy game engine
- ECS game engine in Rust. Great for learning graphics + Rust together.
- cargo-deny
- Check licenses and vulnerabilities of the whole dependency tree.
- Cosmic (Rust desktop UI)
- libcosmic: Rust GUI toolkit for desktop. Ambitious and interesting.
- Cranelift JIT (in Rust)
- A fast JIT compiler in Rust. Learn code generation by reading it.
- Deno (Rust + V8)
- A JS/TS runtime written in Rust. Excellent large-scale Rust case study.
- Diesel — safe SQL ORM
- Compile-time query safety. Opinionated, excellent docs.
- eza (ls replacement)
- Modern `ls` with icons and git status, in Rust.
- fd — find alternative
- Simple, fast, clean Rust. Another excellent small codebase to study.
- Helix editor
- A post-modern modal editor in Rust. Learn its tree-sitter setup.
- Leptos / Yew (Rust web UI)
- Fine-grained reactive Rust web UI frameworks. A taste of a different model.
- napi-rs — Node.js bindings
- Native Node addons via Rust. Popular for JS tooling.
- Nushell (Rust shell)
- A structured-data shell written in Rust. Learn shell design from it.
- Polars — DataFrame in Rust
- Fast streaming DataFrame library. Great for data work in Rust.
- PyO3 — Python bindings
- Write Python extensions in Rust (or vice versa). Well maintained.
- Ratatui (Rust TUI)
- The modern Rust TUI toolkit. Great docs and community.
- reqwest (HTTP client)
- The ergonomic async HTTP client you'll use in most Rust services.
- ripgrep (rg)
- The fast recursive search tool. A great real-world Rust codebase to read.
- Rocket web framework
- Macros, codegen, Rocket.toml. Ergonomic and opinionated.
- ruff — Python linter/formatter
- Blazing fast Python linter/formatter written in Rust. Star codebase.
- Rust Embedded Book
- Rust on microcontrollers. Free book, bare-metal intro.
- Rust GUI ecosystem overview
- Track GUI work via the community page and relevant working groups.
- rust-analyzer
- The Rust language server. Its architecture docs are a good Rust case study.
- RustSec advisory DB
- Advisories for crates. Wire cargo-audit into CI.
- SeaORM
- Async dynamic ORM inspired by Active Record and EF Core.
- Spacedrive (Rust backend)
- Open-source file manager with a Rust core. Interesting architecture.
- SQLx — async SQL toolkit
- Compile-time-checked SQL, like sqlc but native to Rust.
- Tauri (desktop apps)
- Rust backend + web frontend for desktop. Tiny binaries vs Electron.
- Tokio — async runtime
- The async runtime most Rust services use. Learn the runtime first.
- Trunk (web app bundler)
- Zero-config WASM web app bundler for Rust. Pleasant DX.
- UniFFI — mobile FFI
- Ship a Rust core to iOS/Android. Used by Firefox.
- uv — Python package manager
- Ridiculously fast Python env + package manager in Rust. The big trend.
- uv, ruff, polars — Astral stack
- Follow Astral for high-quality Python tooling powered by Rust.
- wasmtime (Rust runtime)
- Production-grade WASM runtime in Rust. Excellent engineering docs.
- wgpu — WebGPU in Rust
- Portable GPU compute. Rust API over Vulkan/Metal/DX12.
- Zellij terminal multiplexer
- Tiled multiplexer in Rust with layouts and plugins. Architecture showcase.
- Zig and Rust interop notes
- See how another systems language solves problems Rust solves. Good contrast.
Security
- CISA Known Exploited Vulnerabilities
- Shortlist of vulnerabilities actually being exploited in the wild.
- CryptoHack
- Modern, gamified cryptography challenges. Free and fun.
- Cryptopals (crypto challenges)
- Classic crypto challenges. Excellent for building real intuition.
- First.org (FIRST)
- Incident response resources, CVSS scoring, and security standards.
- Fuzzing (overview)
- Feeding garbage until something breaks. The highest-yield bug-finding technique in security.
- GitHub Security Advisories
- Curated advisories for popular open-source packages. Check before upgrading.
- Kernel security (Linux)
- Linux kernel security docs: LSMs, hardening, mitigations.
- NVD (CVE database)
- The US National Vulnerability Database. Look up CVEs here.
- OWASP
- The application security foundation. Free, practical guidance.
- OWASP Cheat Sheet Series
- Concise, actionable security cheatsheets. Bookmark this one above all.
- OWASP Top 10
- The canonical list of the ten biggest web security risks.
- Password storage
- How passwords should actually be stored, and why the fast hash you have is the wrong one.
- PortSwigger Web Security Academy
- Free, hands-on security training with labs. Excellent, no cost.
- Secure your app (API security)
- Practical API security clinic. Good for auth, keys and rate limits.
- Security engineering (overview)
- The discipline defined, and how security work differs from security review.
- Sigstore
- Free signing and verification for software supply chains, built on the transparency log model.
- Software supply chain security (SLSA)
- Framework for build integrity. Important for serious engineering orgs.
- Supply chain attack
- How compromising a dependency reaches you, and the controls that actually reduce it.
- Threat model
- What you are defending and against whom, written down before any control is chosen.
- TUF — The Update Framework
- Secure software updates, including rollback and freeze attack protection. The design behind APT.
- Zero trust architecture
- Never trust, always verify. The model most large networks have converged on.
Software Engineering
- 37signals
- Essays and books (Shape Up) from a very opinionated, free blog.
- Awesome (sindresorhus)
- Meta-list of curated awesome lists. The map of all maps.
- Choose Boring Technology
- Dan McKinley on why novelty is expensive. Shapes career decisions.
- coding-interview-university
- A CS degree, self-assembled, for interviews. Huge and free.
- developer-roadmap (source)
- Source repo for roadmap.sh diagrams, incl. system design.
- Exploding Software
- Zachary Voase's classic essay on technical debt. Still the sharpest version.
- free-programming-books
- The best index of free programming books, in dozens of languages.
- Google SRE Book
- What Site Reliability Engineering is, in 23 free chapters.
- Google SRE Workbook
- Incident response, capacity planning, and the human side of SRE.
- Kent Beck archive
- Essays on TDD, simplicity, and the Three/Nine/Twelve fallacy.
- MIT Missing Semester
- Shells, editors, VCS, debugging, TLS, key management. Fills the CS-degree hole.
- Notes on A Philosophy of Software Design
- Notes on Ousterhout's deep-modules book. Pairs with Clean Architecture.
- ossu/computer-science
- Complete standards-based CS curriculum using only free courses.
- ossu/data-science
- Same idea, for data science and ML. All free materials.
- Refactoring Guru
- Best visual explanations of design patterns and refactoring.
- Refactoring: catalog (Fowler)
- The full refactoring catalog with before/after code for each move.
- roadmap.sh
- Interactive developer roadmaps: backend, frontend, DevOps, Android, AI.
- Software Engineering at Google (free)
- Full text of the SWE-at-Google book, free and legally hosted.
- system-design-primer
- Learn how to design large-scale systems. Diagrams included.
- The Architecture of Open Source Applications
- Two free books on the architecture of real systems (Nginx, RabbitMQ...).
- The Book of Secret Knowledge
- Giant one-page dumping ground of tools, cheatsheets and resources.
- The Fuzzing Book
- Everything about fuzzing, free and beautifully typeset.
- The Grug Brained Developer
- Brutally practical, hilarious complexity-reduction guide. Read it, then delete 20% of your code.
- Working Effectively with Legacy Code
- Classic seam-finding techniques. See summaries and reviews.
- Write code that is easy to delete
- On temporary code, over-engineering, and simplicity.
Testing
- Contract testing (Pact)
- Consumer-driven contract testing for services. Free docs and tooling.
- Go test package
- The stdlib testing package. Read its docs once for idiomatic tests.
- Google Test Blog: 'Test Sizes'
- Small, medium and large tests. A framework that outlives trends.
- Google Testing Blog
- Test automation, hermetic tests and code health. Very practical.
- Hypothesis (property-based, Python)
- The most mature property-based library. Learn the ideas from its docs.
- JUnit
- The Java testing framework, and the xUnit model most other runners copied.
- Kent C. Dodds' Testing Blog
- Testing philosophy and confidence. Though JS, the ideas are universal.
- LibFuzzer documentation
- Coverage-guided fuzzing. Learn one fuzzer; the ideas transfer.
- Mocks Are Not Stubs (Fowler)
- The article that clarifies mocking philosophy. Read before you over-mock.
- OSS-Fuzz
- Continuous fuzzing infrastructure used by many open-source projects.
- PIT (mutation testing, Java)
- Mutation testing for the JVM. Raises real coverage quality.
- Playwright
- Cross-browser end-to-end testing with auto-waiting and tracing. The most pleasant E2E experience available.
- Property-based testing overview
- Testing properties over examples, and why it finds bugs that examples cannot.
- pytest documentation
- Fixtures, parametrisation and plugins. The reference everyone actually uses.
- Rust testing
- The Rust book's testing chapter, including property tests and the built-in fuzz target.
- Rust testing guide
- The Book's testing chapter: unit, integration, doc and fuzz tests.
- Stryker (mutation testing)
- Mutation testing: verify your tests fail when the code breaks.
- Test automation (overview)
- The taxonomy of automated testing levels and what each is actually for.
- Testing (overview)
- The levels, the vocabulary, and the economics of where testing effort pays off.
- The Practical Test Pyramid (Martin Fowler)
- How to balance unit, integration and end-to-end tests. Classic.
- Vitest
- Fast unit testing for Vite projects, with first-class TypeScript and watch mode.
Tools & productivity
- BashFAQ and ShellCheck wiki
- Shell pitfalls and static checking. Read the FAQ, it is superb.
- Carbon code screenshots
- Beautiful code images for sharing in docs and slides.
- cheat.sh
- Instant cheatsheets for any command, even obscure ones.
- delta (git diff viewer)
- Syntax-highlighting git diffs. Reviewing code becomes pleasant.
- Diagrams.net (draw.io)
- Free, offline-capable diagram editor. Reliable and open.
- Emacs Doom / Spacemacs
- A modern, reproducible Emacs config. A taste of heavy customization.
- Excalidraw
- Hand-drawn-feeling diagrams. Fastest way to sketch an idea.
- Excalidraw + Figlet + lolcat
- A tiny delightful command that colorizes terminal output. Fun.
- explainshell
- Paste a shell command and see what each part does. Brilliant.
- fish shell documentation
- A modern, friendly, scriptable shell with great docs.
- GNU Bash reference manual
- The complete bash manual. Bookmark for when scripting gets hairy.
- KDE KWrite / Kate docs
- A powerful, hackable text editor with LSP and a great docs site.
- lazygit
- A terminal UI for git. Learn git properly with it.
- Logseq
- Open-source outliner for notes. Great for networked thought.
- Mermaid live editor
- Diagrams from text. Perfect for README files.
- Neovim documentation
- The best-documented modern editor. A masterclass in Lua config.
- Obsidian
- Local-first markdown notes with backlinks. Free for personal use.
- Oh My Zsh / plugin ecosystem
- Popular zsh framework. Or use a minimal, hand-rolled setup.
- pre-commit / lefthook / husky
- Fast git hook runners in Go and Node. Keep your commits clean.
- Pro Git book (free)
- The complete Git book, free online. Read it once, properly.
- regex101
- Build and explain regexes interactively. Plus a cheat sheet.
- starship prompt
- The fast, minimal, customizable shell prompt. Modern default.
- tldr pages
- Community-maintained simplified man pages. Perfect for commands.
- tldraw
- An infinite canvas SDK. Great for building tools and whiteboards.
- Vim Adventures
- Learn vim motions as a game. The fastest way to get fluent.
- Zed editor
- A fast, collaborative editor written in Rust. Worth watching.
- Zoxide (better cd)
- Smart directory jumping that learns your habits. A genuine joy.
Web Performance
- Chrome for Developers (free)
- Free DevTools documentation. Learn the profiler properly.
- Chrome UX Report API docs (free)
- Free docs for field performance data on real users. Very advanced.
- Core Web Vitals (web.dev)
- The free definitive guide to LCP, INP and CLS. Must-read for perf.
- HTTP Archive — datasets (free)
- Free open datasets on real-world web performance. Very interesting.
- HTTP caching (MDN, free)
- Free MDN guide on HTTP caching. A high-leverage perf topic.
- INP — Interaction to Next Paint (free)
- The free deep guide to INP, the responsiveness metric. Must-read.
- Lighthouse documentation (free)
- Free Lighthouse docs. Understand the audits it reports.
- MDN — Web performance (free)
- Free MDN performance guides. Solid and trustworthy.
- Performance.now() conference talks (free)
- Free talks from the web performance conference. Excellent, free.
- Smashing Magazine (free)
- Free long-form web articles on performance, design and accessibility.
- Web Almanac (free report)
- The free annual report on the state of the web. Rich data.
- web.dev — learn performance
- Free structured learning path on web performance from Google.
- web.dev — performance guidance
- Free Google-authored guides on Core Web Vitals and speed. Very good.
AI, Papers & Low-Level Systems
AI Papers & Reading
- AI alignment
- The research problem of making models do what is intended, with the main approaches.
- arXiv — Cryptography and Security (cs.CR)
- Security research, including a large amount of protocol and implementation cryptanalysis.
- arXiv — Data Structures and Algorithms (cs.DS)
- Algorithms and data structures, including the streaming and approximation results worth knowing.
- arXiv — Distributed Computing (cs.DC)
- Consensus, databases, and the systems papers behind most of what runs at scale.
- arXiv — Hardware Architecture (cs.AR)
- Computer architecture, including the accelerator and memory-system papers you need for performance work.
- arXiv — Operating Systems (cs.OS)
- Operating system research, from scheduling to eBPF and unikernels.
- arXiv — Statistics (stat.ML)
- Statistics and statistical machine learning, where the theory of estimation lives.
- Attention (machine learning)
- The mechanism behind the transformer, explained properly with the shapes and the matrix view.
- Awesome AI for science
- AI applied to physics, biology, chemistry and astronomy, with the papers and code for each.
- Awesome AI research papers
- A curated list of seminal and influential AI papers. Useful as a syllabus.
- Awesome machine learning
- 74k stars. The most complete survey of ML libraries, courses, books and tools.
- Awesome production machine learning
- The gap between a paper and a deployed model: tooling for MLOps, monitoring and reproducibility.
- Diffusion model
- How diffusion models generate, and why the reverse process is the whole trick.
- Dive into Deep Learning
- A free book with runnable code for every chapter, in multiple languages. The best way to actually learn the maths of ML.
- Foundation model
- The terminology that replaced big pretrained models, and why it matters for evaluation.
- Generative adversarial network
- The original GAN architecture and the training dynamics that made it unstable.
- Hugging Face transformers
- The de facto model library. The model docs double as excellent technical documentation.
- Interpretability
- The field of opening models up. Good orientation before mechanistic interpretability papers.
- JAX and XLA
- Autodiff plus a compiler that fuses everything. The clearest way to see how hardware constraints shape ML.
- Jensen–Shannon divergence
- The loss used in diffusion models, explained from first principles.
- JMLR — Journal of Machine Learning Research
- Fully open access, no author fees, and consistently high quality. The best ML venue that is free.
- Knowledge distillation
- Compressing a teacher model into a student. The main technique behind small model deployment.
- Kullback–Leibler divergence
- Information-theoretic distance between distributions. Underlies most generative model losses.
- Large language model
- What an LLM is, how it is trained, and the practical limits. Good entry point before the papers.
- Machine learning tooling: PyTorch
- The dominant research framework. Its tutorials and the design of its tensor API are worth studying.
- Mixture of experts
- Sparse conditional computation: why a model can have enormous capacity without proportional compute.
- OpenReview
- Peer review for ICLR and other ML venues, with the reviews public. Read the reviews, not just the papers.
- Perplexity
- What the metric means and why comparing perplexities across tokenisers is meaningless.
- Project Euclid
- Free full text for a huge range of mathematics and statistics journals. An enormous free library.
- Prompt engineering
- What actually works when you cannot change the model, and why it is a weak science.
- PyTorch tutorials, examples and books
- A well-organised list of PyTorch learning material, from first model to distributed training.
- Quantization (signal processing)
- The mathematics behind reducing precision, which is how models get small enough to run.
- Reinforcement learning from human feedback
- RLHF, the technique behind instruction-tuned models, and its documented problems.
- Retrieval-augmented generation
- RAG explained with its failure modes, which is the part most write-ups skip.
- Systems for ML and ML for Systems reading list
- The paper list for doing ML on efficient hardware and hardware for ML systems. Exactly the performance angle.
- Transformer (deep learning)
- Architecture, training, and the original results, with the reference implementation linked.
Compute & Accelerators
- cuBLAS documentation
- The GPU BLAS library, and the algorithm-selection guide that tells you which to call.
- CUDA C++ Best Practices Guide
- How to actually get bandwidth out of a GPU: occupancy, coalescing, memory access patterns.
- CUDA C++ Programming Guide
- The official programming guide. Long, but it is the reference and there is no substitute.
- CUDA Zone — NVIDIA developer hub
- Tutorials, samples and the SDK downloads, all free with an NVIDIA developer account.
- NVIDIA developer blog
- Deep technical posts on GPU architecture, optimisation and numerical computing.
- Open Compute Project
- Open hardware designs for servers, racks and AI accelerators. Real schematics and bills of materials.
LLMs & Models
- AutoAWQ
- Activation-aware weight quantisation, which needs no calibration data and often beats GPTQ.
- AutoGPTQ
- A usable GPTQ implementation with a kernel for fast batched inference on quantised weights.
- Axolotl
- A config file for fine-tuning. Takes the YAML boilerplate out of getting a LoRA run going.
- bitsandbytes
- 8-bit optimisers and 4-bit quantisation, plus the LLM.int8() inference path. Quietly essential for training large models.
- DeepSpeed
- ZeRO, offload and pipeline parallelism. What makes training models far larger than one GPU possible.
- ExLlamaV2
- Very fast local inference over EXL2 quantised models. Often the quickest option on consumer GPUs.
- FastChat
- The training and evaluation platform behind the LMSYS Chatbot Arena leaderboard.
- GPTQ
- Code for the GPTQ paper: 3- and 4-bit post-training quantisation with very little accuracy loss.
- Hugging Face TGI
- Hugging Face's production serving toolkit, with token streaming and tensor parallelism.
- Kaggle
- Datasets, notebooks and competitions. Free, and still the best source of tabular data with a public baseline.
- KoboldAI client
- A long-running, open-source front end for local and remote models, with a strong community.
- LiteLLM
- One interface over every model provider, with a proxy, fallbacks and cost accounting. Solves a real problem.
- LLaMA-Factory
- A unified interface for fine-tuning over a hundred model families, with a web UI. The most complete toolkit here.
- llama.cpp Python bindings
- Python bindings for llama.cpp, with a server mode. The simplest way to call a local model from Python.
- LMDeploy
- Compression and deployment from the InternLM team, with a PyTorch-oriented API.
- MLC LLM
- Universal LLM deployment to phone, browser and TV, compiled with Apache TVM. Remarkable footprint work.
- MLX
- Apple's array framework for silicon. The only framework where a NumPy-like API maps cleanly onto the hardware.
- MS-Swift
- ModelScope's fine-tuning and deployment toolkit, with strong multimodal support.
- Ollama
- Local models in one command, with a clean model library. The lowest friction way to run an LLM yourself.
- ONNX Runtime
- Cross-platform inference for ONNX models. The practical way to ship a model into a C++ or mobile app.
- Open LLM Leaderboard
- Standardised evaluation across open models. Read the version column: the benchmarks are v2 for a reason.
- PEFT — parameter-efficient fine-tuning
- LoRA, adapters and prefix tuning. How you fine-tune a large model on a single consumer GPU.
- safetensors
- A deliberately simple, safe model weight format. Replaces pickle loading, which was a real attack surface.
- SGLang
- Fast serving and structured generation, with a RadixAttention prefix cache that saves real money on shared system prompts.
- TensorRT-LLM
- NVIDIA's optimised inference runtime. The fastest option on their hardware, at the cost of the lock-in.
- tinygrad
- A deliberately tiny framework that is also a readable explanation of what deep learning frameworks actually do.
- Transformers.js
- Running transformer models directly in the browser or Node with WebGPU. The same API as Python.
- TRL — transformer reinforcement learning
- SFT, DPO, PPO and reward modelling in one library. The reference implementation for the post-training methods.
- Unsloth
- Fine-tuning that claims to be twice as fast and use far less memory, by patching the attention kernels.
- WebLLM
- In-browser LLM inference via WebGPU. No server, no API key, everything client side.
- whisper.cpp
- OpenAI's Whisper speech recognition in portable C++, with no dependencies. Speech-to-text that runs anywhere.
Low-Level Systems
- Abseil — Google's C++ libraries
- The hardened C++ base libraries. Reading the string and flat-hash-map code teaches a lot.
- Address space layout randomization
- ASLR, what it defends against, and the bypasses that followed.
- Application binary interface
- What has to match for code to link, and why C has one and Rust did not need it.
- Branch predictor
- How modern CPUs guess, and the Mispredict penalty that makes branchless code win.
- Cache coherence
- MESI and the protocols that keep multi-core caches consistent, with the costs stated.
- Calling convention
- Who passes what, where, and why x86-64 and AArch64 disagree.
- Chips and Cheese
- Reverse-engineering real microarchitectures from performance counters. The best source on how CPUs actually work.
- Circular buffer
- Lock-free ring buffers, the hardest simple data structure in systems code.
- Complex instruction set computer
- The other side of the debate, and why microcode-era designs are not simply 'bad'.
- Computer Architecture: A Quantitative Approach course list
- The readings for a full three-semester architecture course, by Hennessy and Patterson.
- CPython source
- A famous large codebase. The interpreter loop and object model are a good systems read.
- Direct memory access
- DMA, cache coherency problems it causes, and the IOMMU that fixes them.
- Dynamic linker
- How ld.so resolves symbols at runtime, including symbol versioning and interposition.
- Executable and Linkable Format
- The ELF format in detail, from section layout to relocations. The foundation of Unix linking.
- GCC source mirror
- The compiler source. Heavy but rewarding if you want to understand code generation.
- GDB documentation
- The definitive debugger manual. Learning GDB properly is one of the highest-leverage skills available.
- GDB user manual
- The GNU-hosted copy, same content. Start with the data inspection chapters.
- Go source
- A large, very readable systems codebase in one language. The runtime and scheduler are worth studying.
- Google gVisor — sandboxed runtime for containers
- A user-space kernel in Go. A very effective way to understand what a kernel actually does.
- Google Highway — portable SIMD
- Runtime-dispatched SIMD across architectures. The library to read before writing your own.
- Instruction set architecture
- The interface between software and hardware, and the RISC versus CISC split.
- Intel Software Developer Manuals
- The architecture and optimisation manuals, free. The single best source on x86 microarchitecture.
- Interrupt
- Interrupts, exceptions and the top half and bottom half split.
- libbpf
- The standard eBPF userspace library. Read its examples to learn the CO-RE relocation model.
- libuv — the Node event loop
- A compact, well-written event loop and I/O library. About 10k lines and completely readable.
- Linker
- Static versus dynamic linking, symbol resolution, and the whole linking story.
- Linux kernel userspace API guide
- The system call interface in detail, including all the ioctl interfaces.
- Linux man pages
- Every man page, browsable online. The single most useful reference in systems work.
- LLVM source
- A huge, well-organised C++ codebase. Excellent for learning compiler structure.
- Memory barrier
- The acquire and release fences, and the difference between the compiler and the CPU barrier.
- Memory-mapped I/O and port-mapped I/O
- The two ways to talk to hardware registers, and when each is right.
- Microcontroller
- The MCU as a complete computer, and the constraints that shape embedded design.
- Name mangling
- How C++ encodes signatures into symbol names, and what happens when you get it wrong.
- nlohmann/json
- A JSON library written for humans to read. The clearest demonstration of modern C++.
- Object file
- What a compiler actually emits, and what the linker consumes.
- OSDev wiki
- Bare-metal development: bootloaders, memory maps, writing a kernel. Practical, if dated in places.
- Out-of-order execution
- The reorder buffer and the scoreboard, which explain why assembly order is not execution order.
- Pipeline (computing)
- Instruction pipelining, hazards, and why deeper pipelines were eventually abandoned.
- Position-independent code
- PIC, PIC-objects and the GOT, and why shared libraries need them.
- POSIX
- The portable Unix standard, and where the real systems diverge from it.
- Prefetching
- Hardware and software prefetch, and when an explicit prefetch actually helps.
- Protocol Buffers
- The canonical binary serialisation format. Its generated code is a lesson in C++ pragmatism.
- Reduced instruction set computer
- RISC properly explained, with the performance argument, which is not what people assume.
- SCX — sched_ext, a BPF scheduler
- Writing a Linux scheduler in BPF. The clearest example of eBPF doing something real.
- simdjson
- SIMD-parsed JSON reaching gigabytes per second. A superb worked example of hand-written SIMD.
- Speculative execution
- The mechanism and the security implications that followed from it.
- System call
- The user/kernel boundary, the cost of crossing it, and the vDSO optimisation.
- The OpenBSD source tree
- The most readable large C codebase in existence, by deliberate policy. A good C reference.
- Virtual memory
- Paging, TLB walk costs, and the page-table structures at scale.
- Zero-copy
- sendfile, mmap, splice and friends, and the syscalls that avoid copying entirely.
Performance Engineering
- A Philosophy of Software Design (Ousterhout)
- The clearest short book on why complex designs are slow, and how to avoid them.
- ACM Queue
- Long-form articles on systems and performance from the ACM. Blocks bots to a plain client, entirely free.
- AddressSanitizer
- Finds buffer overflows and use-after-free at run time, with a small slowdown. The first tool to reach for in C and C++.
- Amdahl's law
- Why the serial fraction caps your speedup. The formula to quote before proposing parallelism.
- Benchmark (computing)
- What a benchmark does and the ways benchmarks mislead, which is most of the ways.
- Criterion.rs — statistical benchmarking
- Rust benchmarking that detects regressions statistically rather than by eyeballing numbers.
- FlameGraph
- The visualisation Brendan Gregg built that made profiling legible. Start here if you have never used it.
- Floating point operations per second
- What FLOPS actually counts, and why comparing FLOPS between precisions is meaningless.
- Google Benchmark
- The microbenchmarking library to use when you care about nanoseconds and repeatability.
- gperftools
- Google's fast allocators, CPU profiler and heap profiler. The easy way to get started profiling C++.
- Gustafson's law
- The counter-law, showing parallelism can still win when the problem grows. The nuance Amdahl omits.
- LemonBench
- Daniel Lemire's writing on SIMD, bit tricks, branchless code and fast parsers. Practical and deep.
- Little's law
- The relation between latency, throughput and concurrency in a queue. Underused and extremely useful.
- LLVM Memory Sanitizer documentation
- Catching memory errors that do not crash. The most under-used tool in native code development.
- Memory bandwidth
- The wall most modern optimisation hits, and the DRAM hierarchy behind it.
- perf wiki
- The wiki for the Linux perf tool, including event lists and how to read them.
- Performance engineering reading list
- A curated list on the theory and practice of performance work, from latency to throughput.
- probablydance — web performance and Go
- Web Almanac analysis and Go performance work, from the author of Go's own profiler work.
- Roofline model
- Whether your kernel is compute bound or bandwidth bound. The first question to answer when optimising.
- Sanitizer project (all four, and the rules)
- The umbrella project, and the documented limits of what each sanitizer can and cannot see.
- ThreadSanitizer
- Finds data races by instrumenting memory access. Slow, but it is the only reliable way to find them.
- UndefinedBehaviorSanitizer
- Catches undefined behaviour the compiler is otherwise free to assume away. Cheap enough to leave on in production.
- USENIX
- Every USENIX conference paper is free. Systems, performance, security and networking research, all open.
Reverse Engineering
- angr — binary analysis framework
- Symbolic execution, CFG recovery and constraint solving. A research framework that answers questions statically.
- Awesome Frida
- A curated index of Frida resources, scripts and bypass write-ups. The best map of the dynamic instrumentation world.
- BlackHat Asia archives
- Talk archives from a long-running security conference, much of it free. Deep applied content.
- capa — identify capabilities in binaries
- Detects what a binary can do rather than what it is called. The most useful triage tool in malware analysis.
- Capstone
- A multi-architecture disassembly engine with bindings for Python, Rust, Go and Java. Excellent for building your own tooling.
- Chromium source browser
- A very large real-world codebase in C++ with its build files. Useful as a reference when reading decompiler output of compiled C++.
- Detect It Easy
- Identifies compilers, packers and protectors by signature. Instant context when you first open an unknown binary.
- Flare IDA — free decompiler build
- A free IDA-style decompiler for researchers, and the source of the FLARE obfuscation deobfuscators.
- GDB and the binutils docs
- The full binutils documentation: objdump, readelf, nm, strip. The command line tools that make RE scriptable.
- Ghidra — official site and downloads
- The NSA's free decompiler. The scripting API, the decompiler and the processor modules are all public.
- Ghidra Bridge
- A Python bridge to Ghidra, so you can drive the decompiler from your own tooling.
- Ghidra scripting API
- The Java and Python scripting API. Automating a hundred decompiler actions beats clicking through them.
- Learn X in Y minutes
- Quick syntax references for dozens of languages and tools. Not deep, but the fastest way to read unfamiliar assembly-level idioms.
- LIEF — binary parsing library
- Parse and patch PE, ELF and Mach-O files. The library to reach for when you need to modify binaries programmatically.
- LLDB
- LLVM's debugger, the one to use on macOS and for C++ on any platform. A much better default than gdb on C++.
- pefile
- Pure Python PE file parsing. Small, readable, and the basis for most PE tooling you will write.
- RetDec
- A complete open-source decompiler suite: from binary to readable C-like code, with a C++ frontend.
- Reverse engineering
- The field overview, with the legal and ethical context that matters before you take work apart.
- SANS Internet Storm Center blog
- Daily reverse engineering and malware analysis write-ups from practitioners. Consistently the highest signal.
- Triton — dynamic symbolic analysis
- A library for instruction-level tracing and symbolic execution with taint analysis. Excellent for cryptanalysis of binaries.
- Unicorn Engine
- Emulate individual CPU instructions with hooks. The practical way to lift and analyse shellcode.
- x64dbg
- A free Windows debugger with a built-in disassembler and a plugin ecosystem. The standard tool for native RE on Windows.
Anatomy & Physiotherapy
Anatomy
- Amoeba's Anatomy
- Free illustrated anatomy study notes and diagrams, freely shared.
- Anatomy Atlases — cross sections
- Free sectional atlases with labelled CT and MRI cross sections.
- Anatomy Atlases (Michigan State)
- Free digital atlases: sectional anatomy, cross-sections, endoscopy. Scholarly quality.
- Anatomy.app
- Free interactive 3D anatomy and physiology learning, browser based.
- AnatomyQA (Commons)
- An enormous pool of freely licensed anatomical images, diagrams and plates.
- AnatomyTOOL
- Free interactive anatomy diagrams and quizzes, multilingual.
- BioDigital Human
- Free interactive 3D human body with tissue-level detail. Very good for learning.
- BodyParts3D
- Free 3D anatomy viewer with a huge labelled database of human structures.
- Complete Anatomy (3D4Medical)
- Excellent 3D anatomy app with a free tier. Worth trying.
- GetBodySmart
- Free interactive physiology and anatomy tutorials with quizzes.
- GetBodySmart — human anatomy
- Free interactive tutorials on every organ system. Very good for basics.
- InnerBody
- Free interactive anatomy reference with clear explanations per system.
- Kenhub
- Free core content plus quizzes and diagrams. Excellent for visual anatomy.
- Musculoskeletal Key
- Free companion site for musculoskeletal anatomy and pathology textbooks.
- NIH 3D Print Exchange
- Free repository of printable 3D medical models, including anatomy.
- NIH MedlinePlus — anatomy topics
- Free plain-language anatomy explainers for every body part.
- Physiology — StatPearls
- Free authoritative physiology chapters on the NIH Bookshelf.
- Radiopaedia
- The best free radiology reference: cases, anatomy, imaging technique. Essential.
- Radiopaedia — anatomy articles
- Free anatomy articles written by radiologists. Clear and imaging-based.
- Servier Medical Art
- Free, high-quality medical illustrations. CC BY licence, perfect for study notes.
- TeachMeAnatomy
- Free, beautifully illustrated anatomy teaching site. The best free anatomy resource.
- The Anatomy Guy
- Free illustrated anatomy notes and lectures, well organised.
- Visible Body
- Free tier 3D anatomy with good explanations. Paid tier is richer.
- Z-Anatomy (open 3D atlas)
- A complete, free, open-source 3D anatomy atlas. Runs in the browser. Outstanding.
- Z-Anatomy source (open data)
- The free atlas source data and models. CC-licensed, fully open.
Physiology
- Action potential
- The all-or-nothing spike, its propagation, and the refractory period that limits firing rate.
- Balance (ability)
- The vestibular, visual and proprioceptive systems integrated, and what training actually improves.
- Blood
- Composition, functions, and what each component does in oxygen transport and defence.
- Blood pressure
- The measurement everyone screens for, and what the numbers actually mean.
- Bone remodeling
- Osteoclasts and osteoblasts in cycle, and why bone is stronger under load.
- Brain-derived neurotrophic factor
- The protein most associated with exercise improving cognition, and the honest state of the evidence.
- Cardiac output
- Stroke volume times heart rate, and the ceiling that limits aerobic performance.
- Cardiovascular disease
- The leading cause of death worldwide, and the one physical activity most reliably reduces.
- Circulatory system
- Heart, vasculature and blood, and the adaptations that make endurance possible.
- Digestive system
- From ingestion to absorption, and the constraints it places on fuelling a long session.
- Electocardiography
- Reading the electrical activity of the heart, and why athletes get screened for it.
- Endocrine system
- Hormones, glands, and the training responses that are hormonal rather than mechanical.
- Heart rate
- The basics, and why heart rate is the easiest measure and a poor predictor of performance.
- Heart rate variability
- Beat-to-beat variation as a window on autonomic balance. Widely used, frequently over-interpreted.
- Homeostasis
- Negative feedback as the organising principle of physiology, and why exercise is a controlled perturbation of it.
- Hypertension
- The most common cardiovascular risk factor, mostly asymptomatic, mostly treatable.
- Immune system
- Innate and adaptive immunity, and what heavy training does to it.
- Inflammation
- The acute response, and why the same process that rebuilds tissue also damages it.
- Insulin
- Glucose handling, and the reason carbohydrate timing around training is not as simple as it sounds.
- Membrane potential
- The resting potential and how an ion gradient maintains it. Everything neural builds on this.
- Metabolic syndrome
- The cluster that predicts cardiovascular risk far better than any single number.
- Nervous system
- Central, peripheral, somatic and autonomic. The fastest control system in the body.
- Neurophysiology
- Neurons as electrical and signalling devices, at the level of the mechanism.
- Neuroplasticity
- Structural and functional change in response to use. The physiological basis of training and rehabilitation both.
- Neurotransmitter
- The chemical messengers, their receptors, and the pharmacology built on top of them.
- Obesity
- Definitions, mechanisms, and where the evidence for any single intervention is weakest.
- Osteoporosis
- Loss of bone density, the fracture risk that follows, and what actually prevents it.
- Oxidative stress
- Reactive species, the redox balance, and why the exercise antioxidant story keeps reversing.
- Physical activity
- The definitions that matter for research and for guidelines, which are not the same.
- Physical fitness
- The components, and the fact that they are partially independent and often trade off.
- Physiology
- How living systems function, and the levels of organisation the field works at.
- Platelet
- Fragments of megakaryocytes, and primary haemostasis.
- Proprioception
- Position sense without vision, and why it degrades with fatigue and with injury.
- Red blood cell
- Haemoglobin, the lack of a nucleus, and the trade-off that makes them good at gas exchange.
- Respiratory system
- Ventilation, gas exchange, and why VO2 max is limited as much by breathing as by oxygen delivery.
- Sedentary behavior
- Sitting is a distinct exposure with distinct effects, independent of how much you exercise.
- Stroke volume
- How much blood the heart moves per beat, and why it is the variable that actually trains.
- Synapse
- Chemical and electrical synapses, and plasticity as the mechanism of learning.
- Thermoregulation
- Heat production, loss, and the limits of working in the heat.
- Type 2 diabetes
- Insulin resistance, and the unusually strong evidence for exercise as a treatment.
Physiotherapy
- APTA — patient care resources
- American Physical Therapy Association public resources. Some free, some member-gated.
- Canadian Physiotherapy Association
- Free professional resources and public education material on physiotherapy.
- Fitness professionals resources
- Free exercise library with instructions and video, useful for rehab programming.
- Graded exercise & pain neuroscience
- Free overview of the evidence-based approach to persistent pain.
- Injury and rehab protocols
- Free condition-specific rehabilitation frameworks from Physiopedia.
- JOSPT — clinical practice guidelines
- Free, rigorous CPGs for common musculoskeletal conditions. Essential for practice.
- JOSPT (open access)
- Journal of Orthopaedic & Sports Physical Therapy. Many clinical practice guidelines free.
- Journal of Physiotherapy (open)
- Free full-text Australian physiotherapy journal with clinical commentary.
- Open access physiotherapy journals
- Free full-text journal on sports science, exercise and rehabilitation.
- Physio-pedia — special tests
- Index of the special orthopaedic and neurological tests, with descriptions.
- Physiopedia
- The best free physiotherapy resource. Thousands of peer-reviewed pages on conditions and tests.
- Physiopedia — conditions
- Browse Physiopedia by body region and condition. Free, no login needed.
- Physiotherapy Evidence — Pedro
- Free Australian physiotherapy database of peer-reviewed clinical practice guidelines.
- Physiotutors
- Free study guides, cheat sheets and exam content for physiotherapy students.
- Rehab My Patient
- Free printable exercise handouts in many languages. Very practical for patients.
- Rehabilitation measures (ReHabMe)
- Free catalogue of standardised rehabilitation outcome measures and their licences.
- StatPearls — Physical Therapy
- Free authoritative physio chapters on the NIH Bookshelf.
- The Student Physical Therapist
- Free resources for physio students: notes, flashcards and articles.
- WHO — rehabilitation
- Free WHO guidance on rehabilitation services, assistive tech and function.
Radio, Antennas & RF
Antennas
- 4nec3 antenna modelling
- Modern NEC-based antenna modeller with a graphical interface. Far easier to learn than raw NEC input files.
- Antenna measurement with VNA
- NanoVNA: a pocket vector network analyser. Lets you measure S11 and tune real antennas.
- Antenna modelling with openEMS
- Free open-source electromagnetic simulation. Full 3D field simulation, no licence needed.
- Antenna Theory (antenna-theory.com)
- The most complete free antenna reference online. Equations, patterns, and worked designs.
- Antennas for radio frequencies (G4IST)
- Well-written free articles on practical antenna construction and measurement.
- ARRL Antenna Book (free edition)
- The reference work for amateur antennas, from the ARRL. The book is sold, but ARRL publishes extensive free material alongside.
- Cable and connector reference
- Practical reference on coax loss, connectors and why the loss compounds through long runs.
- Fresnel zone (Wikipedia)
- The single most important concept for line-of-sight and satellite link planning.
- Friis transmission equation (Wikipedia)
- The formula behind almost every free-space link budget. Understand it once, use it forever.
- HamSCI — antenna modelling papers
- The amateur radio science community. Modelling tools, weak-signal studies and research archives.
- Horn antenna (Wikipedia)
- The workhorse of the microwave and radio-astronomy world, with aperture theory.
- Ionosphere and propagation (SPARC)
- Real-time ionospheric and solar data, plus the maths of HF propagation. Free and open data.
- K7MEM — Antennas and Electromagnetic Fields
- Rich collection of free antenna calculators, design aids and a very good EM field reference.
- Log-periodic antenna (Wikipedia)
- The wideband directional antenna used for TV, radio and spectrum monitoring.
- NanoVNA firmware and design files
- Open-source firmware and the public circuit design for the NanoVNA, the community's favourite cheap VNA.
- NEC-2 and NEC-4 antenna modelling
- The Numerical Electromagnetic Code is the standard free tool for antenna modelling.
- NEC++ and antenna design tools (GitHub)
- Open-source tooling around the NEC antenna solver, with a usable Python interface.
- Patch antenna (Wikipedia)
- The printed antenna behind every Wi-Fi card and phone. Compact design theory.
- PropPredictor
- Free HF propagation predictions across multiple models. Practical for planning a contact.
- Skywire Technologies (mesh networking)
- Open-source long-range mesh radio. Includes full mesh networking documentation and design.
- VK2ZAY antenna design notes
- Practical, readable antenna design articles with clear diagrams. Excellent teaching material.
- Yagi-Uda antenna design (Wikipedia)
- The classic directional TV and amateur antenna, with the design mathematics laid out.
Radio & Amateur
- ADSB decoding and aircraft tracking
- Free open ADS-B exchange network and documentation. A great real-world radio data project.
- AMSAT — amateur satellites
- The amateur satellite organisation. Free mission data, orbital predictions and design guidance.
- APRS protocol specification
- The official Automatic Packet Reporting System specification. Clear, readable, free.
- APRS-is and LoRa APRS
- LoRa APRS is a modern, low-power, long-range take on APRS. Full open specification.
- ARRL — American Radio Relay League
- The largest amateur radio association. Free operating manuals, band plans and licence exams.
- ARRL Learning (free courses)
- Free structured ARRL courses on antennas, propagation, digital modes and operating.
- Band plans (UKSMG)
- Detailed UK/EU band plans showing exactly which modes are welcome where.
- Contest logging (N1MM+)
- Free contest logging software. Good way to understand real ham radio operating practice.
- CQP contesting resources
- The Contest Club of Poland maintains excellent free contesting and operating resources.
- Direwolf — APRS digipeater
- A complete open-source APRS digipeater and TNC. Learn the protocol by reading this.
- Direwolf decodes AX.25 packets
- Combined with minimodem this is a complete, fully software amateur packet radio station.
- dump1090 — ADS-B decoder
- The reference open-source ADS-B aircraft decoder, pairs with an RTL dongle.
- eCFR — full US radio regulations
- The authoritative, always-current US Code of Federal Regulations, searchable and free.
- FCC Part 15 — unlicensed devices
- The US rules for low-power unlicensed transmitters. Know these before transmitting anything.
- FCC Part 73 — broadcast
- US low-power FM and AM broadcast rules, including the LPFM and Part 15 stations.
- FCC Part 97 — amateur radio
- The US amateur radio rules in full. Small page count, worth reading once.
- fldigi
- Free multi-mode digital communications software covering RTTY, PSK, Olivia, JT65 and more.
- Ham Radio Stack Exchange
- Excellent free Q&A covering theory, operating and equipment across every amateur band.
- HamStudy — free exam prep
- Free, ad-light study material and practice exams for the US amateur licence. Very well done.
- HamTraining.com
- Free complete ham radio course with audio lessons. Covers the whole syllabus from scratch.
- IARU — International Amateur Radio Union
- The international body coordinating amateur radio. Free band plans and contest rules.
- IOTA and DX hunting guides
- Islands on the Air and DX programme information, with free award tracking.
- ITU Radio Regulations
- The international treaty governing all radio use. Free to read and genuinely readable.
- minimodem
- Turns a sound card or SDR into a Bell 202, RTTY, DFSR, SSTV or AX.25 modem in software.
- Ofcom — UK radio regulation
- UK spectrum rules and licensing. The European reference for the UK band plan.
- Pico Ballooning — high altitude balloons
- Build and track real high-altitude balloons carrying amateur radio payloads. Brilliant project.
- QRZ.com — ham callbook and forums
- Callbook lookup plus active discussion forums covering every corner of the hobby.
- Radio spectrum monitoring (SDRadio)
- Software-defined radio reception for broadcast monitoring, with strong community documentation.
- Raspberry Pi as an amateur radio station
- A practical project supplier and reference for building a Pi-based radio and packet station.
- RTTY, PSK and digital modes reference
- Long-running reference for digital mode parameters, frequencies and software.
- Shortwave listening guides
- Database of shortwave stations, schedules and frequencies. Free and detailed.
- Signals Most Wanted (SMW)
- Broadcast DX and radio monitoring community with identification help.
- Stratton — amateur satellite tracking
- Real-time satellite tracking and orbital predictions, free and reliable.
- The Airheads: DMR, D-STAR, P25
- Community reference for digital voice modes, with detailed technical comparisons.
- WSJT-X — weak signal software
- The FT8, FT4 and JT65 decoder that made weak-signal operating mainstream. Free and open source.
- WWV and time signal reference
- How time and frequency are broadcast and why radio standards matter. NIST is the authority.
Radio Frequencies & Bands
- 5G NR frequency bands
- The n1 through n100 band table, including the mmWave bands and their coverage reality.
- Airband
- Civil aviation voice frequencies, tower and ground conventions. Listen with a cheap scanner.
- Amateur radio frequency allocations
- The worldwide amateur allocations with the primary and secondary status of each region.
- ARRL band plans
- What is expected on each amateur band, region by region. Not a legal rule, but the convention.
- Atmospheric duct
- The VHF propagation event that carries signals hundreds of kilometres. Explains a lot of long-distance contacts.
- Bandwidth (in computing and radio)
- Bandwidth in hertz versus in bits per second, and why confusing the two causes bad designs.
- Critical frequency
- The MUF concept properly explained, which is the number every HF prediction turns on.
- Digital Audio Broadcasting
- DAB, the digital successor to FM, and why it occupies a completely different slice of spectrum.
- Digital television
- DVB and ATSC, their modulation choices, and the spectrum each moved into.
- FCC Part 2 — Table of Allocations
- The US allocation table in full. Every band you might transmit on is defined here.
- FCC Part 95 — personal radio services
- CB, FRS and GMRS: the no-licence services most people actually want, with their real limits.
- FCC Universal Licensing System
- Look up any US broadcast, amateur or land-mobile licence and its granted frequencies. Blocks bots, so allow for that.
- Ionosphere
- The layers, their altitudes, and why they reflect HF. Everything about long-distance radio is here.
- ISM radio bands
- The unlicensed bands and their worldwide variations. The frequencies nearly every cheap radio device uses.
- ITU-R V.431 — band nomenclature
- The official definitions of VHF, UHF, SHF and the EHF bands. Settles every naming argument.
- LoRa (overview)
- The chirp spread spectrum modulation, its bandwidth-to-data-rate trade-off, and the regional plans.
- LTE frequency bands
- Every LTE band number with its frequencies, bandwidths and duplex mode. Reference for any cellular work.
- Marine VHF radio
- VHF marine channels, DSC and the channel 16 convention. The most accessible band to monitor legally.
- Microwave (overview)
- Above 1 GHz, where propagation, waveguide and line-of-sight behaviour change character.
- Radio propagation
- The master reference: ground, sky, ionospheric and tropospheric propagation in one article.
- Radio spectrum
- What the spectrum is, how it is divided, and why allocation is a political as much as technical question.
- RSGB band plans
- The UK and European band plans, which differ from the US in several important places.
- Shortwave bands
- The HF band allocations, with usage by region and the schedules worth monitoring.
- Shortwave radio
- The HF bands, ionospheric skip, and the long history of listening to them.
- Skywave propagation
- How a signal hops between ionospheric layers, and why distance and frequency trade off.
- Time signal stations
- WWV, WWVH, DCF77, MSF, JJY and CHU. Trivially receivable on any radio and a good first SDR project.
- Tropospheric propagation
- Why VHF and UHF go much further than line of sight, and the standard models for it.
- Trove — Australian spectrum database
- A free, fully searchable database of every radiofrequency licence issued in Australia. The best public spectrum dataset in the world.
- Ultra high frequency
- 300 MHz to 3 GHz, where cellular, Wi-Fi and most modern radio lives.
- Very high frequency
- The 30–300 MHz range, its propagation quirks, and who uses it.
- Whispering-gallery wave
- The Earth-ionosphere waveguide, and the odd long-distance VHF contacts it produces.
- Wi-Fi 6 (802.11ax)
- The 2.4, 5 and 6 GHz bands, channel widths and the regulatory differences between them.
- WWV — the US time signal station
- The 2.5, 5, 10 and 15 MHz time broadcasts, and how the station's own atomic clocks work.
- Zigbee (overview)
- The 868/915 MHz mesh standard, its channel plan, and why it overlaps so much with LoRa.
RF & Microwave
- 6 GHz and above spectrum use
- US rules for experimental and low-power RF use. Worth knowing if you work above the ISM bands.
- Analog Devices — RF and microwave design resources
- Thousands of free application notes on RF design, amplifiers, ADCs and layout.
- Aviation radio and transponders
- Understanding ADS-B, transponder codes and how aircraft identification actually works.
- Bluetooth Core Specification
- The authoritative Bluetooth specification, free to download. Dense but complete.
- ChirpStack LoRaWAN
- Open-source LoRaWAN network server, complete with clear protocol documentation.
- Ettus USRP hardware resources
- Reference designs and datasheets for research-grade RF capture hardware.
- Impedance matching (Wikipedia)
- From quarter-wave transformers to L-network matching. Essential RF design skill.
- Link budget calculator (RF Wireless World)
- Free calculators for link budgets, path loss, Fresnel zones and EIRP.
- Meshtastic
- Open-source encrypted off-grid mesh radio over LoRa. Full hardware designs and firmware are public.
- Meshtastic firmware (GitHub)
- Fully open-source firmware and hardware designs for a long-range community mesh network.
- Microwave journal and design articles
- Trade coverage with plenty of free technical content on RF and microwave engineering.
- MIMO (Wikipedia)
- Multiple antenna systems, and why they are the reason cellular speeds climbed so fast.
- NIST wireless network security guidelines
- Free government guidance on securing wireless networks. Clear and authoritative.
- Noise figure and cascade (Wikipedia)
- How to think about receiver sensitivity, and why the first amplifier matters most.
- OFDM fundamentals (Wikipedia)
- The modulation behind Wi-Fi, 4G, 5G, DVB and more. The single most important RF concept today.
- Qorvo RF resources
- Free RF design tutorials, reference designs and evaluation board material.
- Radar basics (Wikipedia)
- Ranging, the FMCW and pulse approaches, and how radar differs from communications.
- RF and Microwave design course notes
- Public course materials from a leading RF programme. Search the department for microwave classes.
- RF module certifications (FCC ID search)
- Look up any radio module's FCC grant, band, power and antenna requirements. Very useful before building.
- RF Wireless World
- Enormous technical library on RF, microwave, antennas and wireless. Effectively a free textbook.
- S-parameter basics (Bowers)
- Skyworks' free app notes on S-parameters and measurement are the clearest practical introduction.
- Sigfox and LPWAN overview
- Low-power wide-area networking, and the trade-offs between LoRa, Sigfox and NB-IoT.
- Software Defined Radio on Wikipedia
- Solid starting point for the whole SDR concept, with a good reading list.
- Spectrum sensing and cognitive radio
- How radios are being designed to detect and share spectrum dynamically. Good frontier reading.
- The Things Network (LoRaWAN)
- Open-source LoRaWAN stack and network server. A great, well-documented IoT radio stack.
- Transmission lines (Wikipedia)
- Why coax behaves the way it does, from VSWR to characteristic impedance. Foundation knowledge.
- VSWR and return loss (Wikipedia)
- The two numbers every radio link is judged by, explained properly.
- Zigbee Alliance
- Specifications for the Zigbee mesh standard, including many free public documents.
Satellites & Space
- CelesTrak SATCAT
- Machine-readable satellite catalogue data, ideal for scripting your own tracker.
- Celestrak satellite catalogue
- Authoritative free catalogue of every satellite in orbit, with orbital data in standard formats.
- Deep Space Network (NASA)
- NASA's three giant dish antennas and the open documentation of how deep space comms work.
- ESA Earth observation resources
- Free imagery and open data from the Copernicus Sentinel fleet, with full acquisition documentation.
- GNU Radio satellite tracking
- Python helpers for pointing your dish and decoding satellite telemetry in GNU Radio.
- GSL — GNU Scientific Library
- Free C library for numerics, useful for the maths behind propagation and orbital work.
- Hack-A-Sat (US Space Force)
- Annual competition where you write code to take control of real satellites. Open challenges each year.
- NOAA weather satellites
- The polar-orbiting weather satellites you can receive yourself with an SDR and a simple antenna.
- Predicting satellite passes — maths
- The six numbers that define any orbit. Learn these and you can track anything by hand.
- Satellite tracking with Python (Skyfield)
- A well-documented Python library for accurate satellite position prediction. Excellent for learning orbital mechanics.
- SatNOGS — open source satellite ground station
- A fully open-source ground station: hardware, firmware and software. Brilliant project to read and build.
- SatNOGS community forum
- Friendly, active community where you can ask about building a ground station from scratch.
- SatNOGS software (GitHub)
- The open-source mission control software, the antenna rotator and the satellite database.
- SSTV — slow scan television
- A legitimate, long-established amateur mode for sending images over radio. Great SDR entry point.
- TLE and orbital data explained
- Every satellite in Celestrak is described by two lines of data. This explains what they mean.
SDR & Radio hacking
- 5G NR — New Radio
- The 5G air interface, and how it differs structurally from LTE.
- Amplitude modulation
- AM from the envelope detector up. The first modulation anyone learns, and still everywhere.
- Base station (overview)
- What a base station actually is, its hardware, and how it differs from a repeater.
- Cell Tower Mapper (FCC)
- Crowdsourced cell tower locations. Useful context for understanding cellular coverage.
- Cellular network (overview)
- How cells, towers, handover and frequency reuse fit together. Read this before anything else in the category.
- CubicSDR
- Another excellent open-source SDR receiver, cross-platform and beginner friendly.
- Direction finding
- How you locate a transmitter: TDOA, angle of arrival, and phased arrays.
- E-UTRA radio interface
- The LTE radio interface itself, with the modulation and channel structure GNU Radio's gr-lte implements.
- Electronic warfare
- The wider field around signal intelligence: electronic attack, protection and support.
- Ettus Research — USRP radios
- The research-grade SDR standard. USRP hardware plus open UHD driver, used by universities worldwide.
- FCC ASR / license search
- Look up any US cell tower, its owner, license and effective radiated power from the official register.
- Flipper Zero
- Open-source hardware radio tool for sub-GHz, NFC, RFID and more. Firmware and schematics are public.
- Flipper Zero firmware (GitHub)
- Fully open firmware you can build yourself. A genuine reference implementation for embedded radio UIs.
- Frequency modulation
- FM theory including Carson's rule, which tells you the bandwidth a signal needs.
- Frequency-hopping spread spectrum
- FHSS and Bluetooth's older hopping scheme. Bluetooth LE is the interesting successor.
- GNU Radio Companion (GRC)
- The graphical front end to GNU Radio. Drag-and-drop flowgraphs instead of writing signal processing by hand.
- GNU Radio tutorials (official wiki)
- Official walkthroughs from first flowgraph to filters, modulation and receiver design.
- GNURadio SIGINT and radio intel wiki
- GNU Radio's own notes on signal intelligence, direction finding and receiver architecture.
- go-donut — position-independent shellcode loader in Go
- Generates a raw shellcode loader from a Go binary, so you can test injection against your own processes. Well documented.
- GOES weather satellites
- The geostationary weather satellite fleet, including the LRIT/HRIT downlink formats.
- gr-gsm — GSM receiver in GNU Radio
- A working GSM receiver you can run yourself. The clearest way to understand how a cellular handset actually talks to the network.
- gr-ieee802-11 — 802.11 in GNU Radio
- Full 802.11 receiver and transmitter in GNU Radio. The most complete free Wi-Fi SDR implementation.
- gr-lte — LTE receiver in GNU Radio
- The LTE equivalent of gr-gsm. Reads the control channel of a real LTE cell from a HackRF or LimeSDR.
- gr-osmosdr — SDR support for GNU Radio
- Osmosdr's driver, giving GNU Radio a single interface for a dozen different SDR hardware options.
- gr-radar — radar and doppler in GNU Radio
- Passive and active radar processing, including a real-time Doppler radar you can point at a wall.
- gr-satellites — satellite decoding in GNU Radio
- Decodes telemetry from weather satellites (NOAA APT) and amateur radio satellites. Very satisfying.
- gr-satnogs — SatNOGS baseband
- The GNU Radio blocks that let a SatNOGS station decode satellite telemetry automatically.
- HackRF One firmware (GitHub)
- Full open-source firmware and host tools for the HackRF. Actively developed by the community.
- inspectrum — offline signal analysis
- Reverse-engineers unknown modulations from recorded samples. Pairs perfectly with URH.
- LimeSDR
- Open-source SDR with real transmit and receive, plus an onboard FPGA. Very hackable.
- LTE (telecommunication)
- The full LTE description: E-UTRA, the radio interface, and the architecture diagrams worth memorising.
- LTE Attack Toolkit
- Not a radio tool, but the best place to start for inspecting and manipulating network traffic in depth.
- Minimum-shift keying
- MSK and GMSK, the modulation behind GSM and most modern packet radio.
- Multimon-ng
- Decodes dozens of analog and digital modes including APRS, AFSK, DTMF and POCSAG.
- Numbers station (overview)
- Shortwave stations broadcasting coded numbers. Fascinating history and a real use for an HF receiver.
- Nyquist rate
- The sampling theorem every SDR decision depends on. Understand it and aliasing stops surprising you.
- Open Wireless Security Lab (OWSL)
- Reference material on wireless security research, including the annual WPA test suite.
- OpenIQ — open-source LTE/5G radio
- OpenAirInterface: a complete, readable 4G/5G stack you can run and inspect. Excellent for learning how cellular radio actually works.
- OpenLTE — open-source LTE stack
- A complete software LTE eNodeB and UE. Lets you run your own 4G cell and see exactly what a handset transmits.
- Phase-shift keying
- BPSK and QPSK, and why phase is what carries the bits.
- Phased array
- Beam steering and beamforming, which is what makes direction finding practical.
- Quadrature amplitude modulation
- QAM: how more bits per symbol get sent, and what the trade-off in noise actually is.
- Radio atmospheric signal
- Sferics, whistlers and sprites detected with ordinary radio receivers. A cheap way into real atmospheric science.
- Radio receiver (overview)
- Receiver architectures, from superheterodyne to direct conversion and software defined.
- RFCat — Radio Frequency Control Toolkit
- Python tooling for talking to cheap nRF52 and CC1101 radio boards. The entry point for sub-GHz experimentation with your own hardware.
- RTL_433 — decode 433 MHz sensors
- Decodes common cheap wireless sensors (weather stations, doorbells, remotes) from an RTL dongle.
- RTL-SDR dongle (official, rtl-sdr.com)
- Start here if you just bought a dongle. Drivers, sample rates, and what you can legally receive.
- rtl-sdr source (osmocom)
- The reference open-source driver and utilities for RTL2832U-based dongles.
- rtl-sdr.com — the RTL-SDR blog
- The definitive source for RTL-SDR dongles: reviews, antenna advice, and a huge archive of real projects.
- SDR++ — modern SDR receiver
- A fast, flexible multi-SDR receiver with a polished plugin architecture. Excellent for beginners.
- SDRangel
- Multi-purpose receiver for ISM bands, weather satellites, ADS-B and more.
- Shannon–Hartley theorem
- The theoretical maximum data rate of a noisy channel. The other half of understanding SDR trade-offs.
- Shuhari — SDR signal collection
- A well-regarded open-source project for collecting and classifying radio signals into a database.
- SigDyl / DSD — digital speech decoders
- Digital Squelch, the reference decoder for unencrypted digital voice used by public safety and amateur radio.
- Signal identification (sigidwiki)
- A community wiki of signal waveforms and identifications. Invaluable when a capture is unknown.
- Signal modulation
- The master reference table of every modulation scheme, with its constellation diagrams.
- Signal strength in telecommunications
- dB, dBm, EIRP and the difference between them, which trips up everyone once.
- Signals intelligence
- The discipline itself: SIGINT, COMINT, ELINT and OSINT, with history and method.
- SoapySDR
- A common abstraction layer so SDR code works across HackRF, RTL, LimeSDR, USRP and others.
- Spread spectrum
- The general principle behind CDMA, FHSS and DSSS, all of which appear in cellular and GPS.
- srsRAN
- A 4G/5G radio access network in C++, used for research and for testing your own equipment.
- Synthetic-aperture radar
- How radar builds resolution from motion. Clear diagrams and a satisfying idea.
- Time of arrival
- The core localisation technique, and the maths behind timing accuracy.
- Ubertooth One
- Open-source Bluetooth monitoring and research hardware with full firmware available.
- UHD driver ( Ettus, open source)
- The open-source driver behind USRP radios. Also the API most other SDR tools build on.
- Universal Radio Hacker (URH)
- Complete offline wireless protocol analysis and reverse engineering. Open source, works without a radio.
- Weather satellite
- The polar-orbiting satellites you can receive directly, with the frequencies and equipment.
Tech Leadership & Decisions
Architecture Decisions
- ADR — Architectural Decision Records
- The decision-record pattern: record the context, the options and the consequences, and never rewrite history.
- arc42 — architecture documentation template
- A free, opinionated template for architecture docs that answers the questions reviewers actually ask.
- AWS Well-Architected Framework
- Free, opinionated review checklists across reliability, security, cost and performance.
- Cost-benefit analysis
- The arithmetic behind build-versus-buy, rewrite-versus-extend, and every staffing argument.
- Distributed computing
- The fallacies, CAP, and the fact that remote calls are always slower than you assume.
- Domain-driven design
- Bounded contexts, aggregates, ubiquitous language. Heavyweight, and the best tool for complex business logic.
- Enterprise architecture
- The discipline, its history and its perennial problem of being about diagrams rather than decisions.
- Fault tolerance
- Redundancy, failover and the difference between tolerating a fault and hiding it.
- Fowler — Microservices
- His architecture articles: Microservices, MonolithFirst, BranchByAbstraction. The reasoning matters more than the conclusions.
- Google Cloud Architecture Framework
- The same idea from Google, with the operational maturity model being the useful part.
- High availability
- What the number actually means, the maths of error budgets, and why the last nine is a different problem.
- High Scalability
- A huge archive of real system architectures with actual numbers. Best single source for prior art.
- Jepsen analyses
- Kingsbury's empirical tests of database consistency guarantees. The most credible writing anywhere on when databases lie.
- Load balancing
- The algorithms and why the least-connections rule beats round-robin in practice.
- Microsoft Azure Architecture Center
- Reference architectures, patterns and anti-patterns, free and specific enough to act on.
- Request for Comments
- The RFC process, its origin, and what makes a public design document actually work.
- Risk management
- Identifying, quantifying and accepting risk. The missing half of most architecture reviews.
- Scalability
- Vertical and horizontal, and the awkward truth that most systems do not need to scale.
- Specification (technical standard)
- What a specification is for, and why an RFC is not a contract.
- Systems design
- The discipline of designing whole systems, and the vocabulary for talking about constraints.
Negotiation & Communication
- Active listening
- The technique, its steps, and its documented limits. Underrated in technical settings.
- Agile software development
- The manifesto, and twenty years of evidence about when it helps and when it is cargo-culted.
- Assertiveness
- Stating a position without either collapsing or escalating. The middle option most people never find.
- Code review
- The practice, its formats, and the research on what actually catches defects.
- Communication
- The field, from Shannon onward. Useful mainly for seeing how much is assumed.
- Conflict resolution
- The methods, and why most technical disputes are not really about the technology.
- Distributed version control
- Git, and the workflow design that decides how much conflict your team will have.
- Emotional intelligence
- The construct, and the decades of debate over whether it predicts anything.
- Empathy
- Cognitive and affective empathy, and the evidence that the two are barely correlated.
- Extreme programming
- The practices that preceded agile, and the ones that quietly survived it.
- Harvard Program on Negotiation
- The research programme behind Getting to Yes. Free articles on method, not just theory.
- Ink and Switch — Ambidextrous notebook
- Kasparov's ambidexterity applied to teams: exploit the known while exploring the unknown. The clearest strategy essay there is.
- Interpersonal communication
- How meaning is actually negotiated between people, and where it breaks down.
- Kanban
- The original Toyota system and its software adaptation, which are not the same thing.
- Laws of UX
- Nielsen's heuristics with a modern visual treatment. Free, and the fastest way to fix interface decisions.
- Mediation
- Third-party resolution, and what mediators actually do that parties cannot.
- Negotiation
- The process defined, and the distinction from selling, which is usually the mistake.
- Nonverbal communication
- Body language, tone and silence. The part of a difficult conversation you cannot write down.
- Pair programming
- The practice, its formats, and the studies on when it actually pays off.
- Persuasion
- How argument and rhetoric change belief, and the limits of the ethical version.
- Plain language
- Writing that the intended reader can act on. The most useful editing principle there is.
- Rhetoric
- Ethos, pathos, logos. Two thousand years of material on making an argument land.
- Scrum
- The framework, the evidence on it, and the failure modes everyone recognises.
- Technical writing
- Explaining systems to people who will act on it. Underrated relative to how much of engineering is this.
- Ten usability heuristics
- The ten, stated precisely. The one article to read before designing any interface.
Tech Leadership & CTO
- Abstraction (in computer science)
- Why abstraction is the core tool and also the main source of accidental complexity. Read alongside Ousterhout.
- Cal Newport
- Deep Craft on software craft, management and attention. His books are the standard for serious engineering careers.
- Chief information officer
- The sibling role, and how CIO and CTO responsibilities overlap and differ.
- Chief technology officer
- The role, its history and how the job has changed as technology strategy matured.
- Cognitive bias
- The systematic ways judgement goes wrong. The most useful one for architecture review is escalation of commitment.
- Decision-making
- The research literature on how decisions actually get made, and why intuition fails under pressure.
- Engineering management (overview)
- The discipline defined, and the technical-versus-people tension that makes it hard.
- Ink and Switch
- Product thinking for engineers. Puts technical strategy next to product judgement, which is the CTO's actual job.
- Ink and Switch — Ambidextrous
- Garry Kasparov's ambidexterity argument applied to product strategy: exploit the known, explore the unknown.
- Joel Spolsky's wiki (Joel on Software)
- Spolsky's business-process wiki. Sharp, opinionated and dated in places, but the vocabulary came from here.
- LeadingDev
- Long-form articles on technical leadership. Much of it is paywalled, but the free articles are genuinely good.
- Paul Graham's essays
- Essays on startups, hiring and judgement, decades of them. The most quoted writing on building companies.
- Software design
- The discipline defined, with the trade-offs made explicit rather than assumed.
- StaffEng
- Guides for the staff-plus track: what the role is, what it is not, and how to get it. The clearest writing on the topic.
- Team Topologies — key concepts
- Stream-aligned, platform, enabling and complicated-subsystem teams, plus the interaction modes. The most useful reframe of team structure in years.
- Technical debt
- Ward Cunningham's original framing and the years of argument since. Central to every prioritization conversation.
- Trade-off
- Every technical decision is a trade-off against something. Naming the thing you gave up is most of the work.
Astronomy & Biology
Astronomy
- AAS — American Astronomical Society
- Free astronomy news, job listings, and community resources.
- AstroBites
- Free graduate-student-written astronomy articles for everyone. Beautifully clear.
- Astrophysics Data System (ADS)
- NASA's bibliographic database for astronomy. Free, with full-text links.
- Bad Astronomy
- Phil Plait's blog: astronomy, science communication, and why things blow up.
- Cosmology — Planck results
- ESA Planck mission: the CMB and its cosmological parameters. Free data.
- Cosmology — Sean Carroll notes
- Free cosmology and relativity lecture notes from a working theorist.
- Dark Energy Survey
- The DES collaboration site. Free data and explainers on dark energy.
- ESA Gaia — star census
- Positions and proper motions of over 1.8 billion stars. Free data.
- ESA/Hubble images
- Free high-resolution Hubble image archive. Publicly available.
- ESA/Webb
- The ESA side of JWST. Full image archive and science explainers.
- ESA/Webb image archive
- Free JWST image and data release. Spectacular and current.
- ESO — European Southern Observatory
- VLT and ALMA images and science. Free high-resolution pictures.
- ESO — image archive
- Free ESO image archive from the VLT and ALMA. Public access.
- ESO / IAU — Astronomy Cast
- Free weekly podcast interviewing working astronomers. Excellent.
- Exoplanet Archive (NASA)
- Every confirmed exoplanet with parameters. Free, canonical data source.
- Heavens-Above — satellite passes
- Free predictions for ISS, satellites and deep-sky objects.
- Hubble Space Telescope
- The Hubble site's public pages: images, science, history. Free.
- IAU — naming and education
- Free International Astronomical Union resources and official naming rules.
- In-The-Sky.org
- Free sky atlas and satellite pass predictions, very detailed.
- Katie Mack — cosmology
- Cosmologist on the early universe and the multiverse. Free resources and talks.
- Minor Planet Center
- The official registry of asteroids and comets. Free.
- NASA
- Missions, images, discoveries. Everything free and public domain-ish.
- NASA — Mars exploration
- Free Mars science, imagery and mission data from NASA.
- NASA Webb Space Telescope
- Images and data from JWST, plus excellent explainers. Free.
- Sean Carroll's blog
- Physics and cosmology commentary from a leading theorist. Very good.
- Seasons of the Moon
- Free blog with a lunar observing guide each month. Lovely for beginners.
- Sky & Telescope — observing
- Practical observing guides. Some content free.
- Vera Rubin Observatory
- LSST. Free science, images and data access information.
- Zwicky Transient Facility
- Public transient survey. Free alerts and imagery.
Biology
- Allen Institute for Brain Science
- Open science on brain structure and function. All data free.
- Biodiversity Heritage Library
- Massive free archive of historic biology and medicine books and journals.
- BioInteractive
- Free HHMI classroom resources and videos. Very high production quality.
- Biology Stack Exchange
- Community Q&A for biology. Good for quick, sourced answers.
- BioPython
- Free open-source Python toolkit for bioinformatics. Great for scripting.
- BrainFacts (Society for Neuroscience)
- Free neuroscience explainers and resources from the SfN. Excellent.
- EMB-EBI training
- Free online courses in bioinformatics, cheminformatics andEMBL-EBI tools.
- Freesurfer — brain imaging
- Free open-source cortical surface visualization suite for fMRI data.
- Human Genome Project (archive)
- Free account of the HGP and its data — a landmark in open science.
- Human Protein Atlas
- Free tissue and cell-level expression of every human protein. Excellent resource.
- iBiology (Talks)
- Free video talks with working scientists. Repeated by working biologists.
- IQ-TREE 2 — phylogenetics
- Free open-source phylogenetics software with excellent documentation.
- Khan Academy — Biology
- Free clear biology from molecules to organisms to ecology.
- NCBI — National Center for Biotechnology Information
- PubMed, PMC, GenBank, Gene, Datasets, Bookshelf. Free, and the hub of biology.
- NCBI Bookshelf — Genetics
- Free authoritative medical genetics reference on the NIH bookshelf.
- NHGRI — genetics education
- Free authoritative fact sheets on genomes, genes and genetic conditions.
- OpenStax Concepts of Biology
- Free non-majors biology text, shorter and very accessible.
- UniProt
- The universal protein knowledgebase. Free, canonical, with an API.
- Wellcome Collection
- Free digital library of health, medicine and biology history. Beautiful scans.
- YourGenome
- Free Wellcome resource explaining genomics terms and technologies. Excellent.
Physics & Chemistry
Chemistry
- ACS — free chemistry resources
- Free American Chemical Society education and outreach material.
- Avogadro — open source chemistry
- Free open-source molecule editor and builder. Cross-platform, no cost.
- Avogadro (Molecule Editor)
- Free open-source molecule editor and builder. Cross-platform.
- ChEBI — Chemical Entities of Biological Interest
- Curated ontology of biologically relevant chemicals, freely available via API.
- ChemBK
- Free Chinese-English chemistry dictionary and compound reference.
- ChEMBL
- Free database of bioactive molecules and their targets. Drug discovery data.
- ChemCollective
- Free virtual labs and simulations for chemistry. Good for visualization.
- ChemDoodle Web Components
- Free chemical drawing and structure recognition in the browser.
- Chemguide
- UK exam-board chemistry explained clearly and honestly. Free, no ads.
- ChemSpider
- Free chemical structure search aggregating many databases.
- ChemTube 3D
- Interactive 3D animations of chemical structures and reactions.
- CODATA — NIST reference constants
- The official reference values used by all of science. Essential.
- CODATA — reference data
- The international committee for reference data in physics and chemistry.
- Compound Interest
- Beautiful illustrated chemistry explainers. Superb for building intuition.
- Crash Course Chemistry
- Fast 10-minute lessons on every chemistry topic. Great for revision.
- IUPAC — Periodic Table of Elements
- The official current periodic table from the international authority.
- IUPAC Gold Book
- The official definitions of every chemical term. Free, authoritative, searchable.
- Jmol / JSmol — 3D molecules
- Free open-source molecular visualization in the browser via JSmol.
- Khan Academy — Chemistry
- Free, very clear chemistry from atoms through equilibrium. Great for building intuition.
- LearnChemE
- Free digital resources for chemical engineering education, developed by MIT.
- MIT 5.111 — Principles of Chemical Science
- Free MIT intro chemistry/quantum course with full lecture videos.
- MIT 5.12 — Organic Chemistry I
- Free MIT organic chemistry lecture course.
- MIT OpenCourseWare — Chemistry index
- Browse every free MIT chemistry course: 5.11 to 5.43.
- MolView
- Free 3D molecule viewer in the browser. Inspect any structure instantly.
- NIST Chemistry WebBook
- Authoritative thermochemical and spectroscopic data. The reference for physical data.
- Open Chemistry LibreTexts index
- Browse every free chemistry textbook by topic: organic, physical, analytical, bio.
- OPSIN — name to structure
- Free Cambridge service that converts chemical names into structures. Brilliant.
- Professor Dave Explains
- Free full university chemistry and physics course notes, clearly explained. Excellent.
- PubChem
- Free NIH database of 100M+ compounds: structures, properties, bioactivity, safety.
- Purdue OWL — APA/MLA guide
- Free writing lab: citation guides, sample papers, and academic writing help.
- Royal Society of Chemistry
- Chemistry research, education and the flagship magazine. Much free.
- The Organic Chemistry Tutor
- Very clear organic chemistry problem-solving videos. Best free Ochem tutor.
- Theodore Gray — The Elements
- Free interactive periodic table with real element samples and videos.
- WebElements
- Free periodic table with detailed data on every element. Reliable reference.
- Wikipedia — Portal: Chemistry
- Well-curated entry points into every chemistry subfield.
Hydrogen
- Ammonia
- The molecule most hydrogen ends up in, and the obvious carrier for a hydrogen economy.
- Ammonia production
- Industrial routes and their energy costs, and why cracking ammonia is much harder than people assume.
- Blue hydrogen
- Reforming with carbon capture. The claim rests almost entirely on capture rates nobody has demonstrated at scale.
- Catalytic reforming
- Where hydrogen comes from as a by-product, and why that matters for refinery emissions.
- Coal liquefaction
- Liquid fuels from solid coal. A reminder that synthetic liquid fuel is not a new idea.
- Deuterium oxide
- Heavy water specifically, and neutron moderation.
- DOE — Fuel Cell Technologies Office
- The US programme office, and a lot of readable technical material on electrolyser cost.
- DOE — Office of Clean Energy Demonstrations
- Funds the large demonstration projects. The project list shows what is actually being built.
- Electrolysis of water
- The industrial chemistry version, with electrolyte choices and cell designs.
- Energy density
- Volumetric versus gravimetric, and the numbers that decide whether a use case is viable at all.
- European Commission — climate action
- Where hydrogen is placed in the EU decarbonisation targets, which is the honest test of its role.
- European Commission — energy
- The hydrogen strategy, the TEN-E network, and the regulatory side of the European hydrogen economy.
- Fuel cell
- Converting chemical energy to electricity directly, which is the entire reason hydrogen is interesting.
- Green hydrogen
- Electrolysis from renewable electricity. Colour-coded, which is less rigorous than the labelling suggests.
- Haber–Bosch process
- Ammonia from hydrogen and nitrogen, the process that made both fertiliser and the twentieth century possible.
- Heavy water
- D2O, its small physical differences, and why those differences run reactors.
- Hydrogen
- The element, its physical oddities, and the overview of every route to making it.
- Hydrogen bond
- Why hydrogen, water and ice behave the way they do, and why ammonia can carry hydrogen at all.
- Hydrogen burning
- The flame chemistry, including the low emissivity that makes hydrogen fires hard to see.
- Hydrogen economy
- The case for and against carrying energy as hydrogen, and where the losses land.
- Hydrogen fuel
- Ammonia, methanol, hydrides and LOHC as carriers, and what each costs in round-trip efficiency.
- Hydrogen production
- All the routes compared: reforming, gasification, electrolysis, and their inputs.
- Hydrogen storage
- Compression, liquefaction, materials and ammonia. The hardest part of the whole hydrogen story.
- Intermolecular force
- Dispersion, dipole and hydrogen bonding. The hierarchy behind boiling points and miscibility.
- IRENA
- The renewable energy agency, with the serious analysis and cost data on green hydrogen projects.
- Isotopes of hydrogen
- Protium, deuterium and tritium, and why the isotopic heavy water industry exists.
- Liquefaction
- Cooling to a liquid at 20 K, the energy cost of it, and why hydrogen is harder than methane.
- Liquid hydrogen
- The physical properties, and the boil-off problem that dominates the tank design.
- Metal hydride
- Reversible solid-state storage, and why the kinetics are worse than the thermodynamics.
- Methane
- The molecule the hydrogen economy mostly reduces to, and the reason for the interest in e-fuels.
- Molten carbonate fuel cell
- Good for combined cycle plant, and sensitive to CO2 contamination in a useful way.
- PEM electrolyzer
- Proton exchange membrane. Fast response, pure output, expensive catalysts.
- Phosphoric acid fuel cell
- The mature stationary design, and the one with the real field history.
- Proton-exchange membrane fuel cell
- The automotive design, and exactly where the platinum and the water go.
- Sabatier reaction
- CO2 plus hydrogen to methane. The reaction any e-fuel or synthetic hydrocarbon ends with.
- Solid oxide fuel cell
- High-temperature, tolerates almost any fuel, and slow to start.
- Specific energy
- Energy per unit mass. Hydrogen wins it by a factor of three over petrol, which is the whole argument.
- Steam methane reforming
- Still how about 95% of hydrogen is made. Extremely cheap, and extremely carbon-intensive.
- Synthetic fuel
- Hydrocarbons from hydrogen and captured carbon. Closing the cycle at a terrible energy cost.
- Water electrolysis
- The reaction, the thermodynamics, and the overvoltage that makes it cost more than the ideal.
Physics
- 3Blue1Brown — calculus
- Free visual calculus. Genuinely the fastest way to learn derivatives and integrals.
- 3Blue1Brown — linear algebra
- The best visual explanation of linear algebra. Prerequisite for QM.
- American Institute of Physics
- Free physics news, education resources and career guidance from AIP.
- APS Physics — journals and news
- American Physical Society: free news, journals, and career resources.
- David Tong — Physics lectures
- Cambridge's free lecture notes on QM, relativity, particle physics, condensed matter. Superb.
- David Tong — String Theory notes
- A complete free string theory course, famously rigorous and approachable.
- Einstein Online
- Max Planck Institute's free intro to relativity, black holes and gravity. Outstanding.
- Fermilab — particle physics explained
- Free plain-language particle physics explanations from Fermilab.
- Feynman Lectures — tips on reading
- The official reading guide to the Feynman Lectures. Start here before diving in.
- IOP — Physics Education
- Free teaching resources and journals for physics educators.
- IUPAP — physics education
- International Union of Pure and Applied Physics. World Physics Day resources.
- John Preskill — quantum computing course
- Free quantum information and computation course. The definitive free resource.
- MinutePhysics
- Short, accurate physics explainers. Perfect for building intuition fast.
- MIT 8.04 — Quantum Physics I
- Zwiebach's clean, complete free quantum mechanics course. Start here for QM.
- MIT 8.05 — Quantum Physics II
- Free QM II: identical particles, spins, time-independent perturbation.
- MIT OCW — Quantum Physics III
- Free advanced QM: formalism, angular momentum, many-body. Excellent problem sets.
- MIT OCW — Vibrations and Waves
- Free MIT course on oscillations, waves and normal modes. Lewin lectures included.
- Morin — Problems and Solutions
- David Morin's free physics problem sets and notes. Brilliantly chosen problems.
- OpenStax University Physics Vol 2 — waves
- Free waves, optics, electricity, magnetism and thermodynamics.
- OpenStax University Physics Vol 3 — quantum
- Free quantum mechanics, atomic physics and nuclear physics chapters.
- Particle Data Group — reviews
- Free authoritative reviews on particle physics, including student-level summaries.
- Perimeter Institute
- Blue-brick theory centre in Canada. Free lectures, interviews and outreach.
- Physics 8.01 / 8.02 collection
- Browse the free MIT classical mechanics course list and materials.
- Physics Girl
- Serious physics with practical experiments. Very good at making things intuitive.
- Physics Stack Exchange
- Rigorous Q&A on every physics subfield. Search before asking; answers are excellent.
- Physics: Principles with Applications
- Another free OpenStax physics title, with real-world clinical applications.
- Physics.SE question index
- Browse the best quantum mechanics questions and answers by tag.
- Srednicki QFT — official free copy
- The free official site for Srednicki's Quantum Field Theory textbook.
- Steve Mould
- Physicist who makes beautiful counterintuitive demos. Excellent physics intuition.
- Susskind — Theoretical Minimum
- Free lecture series: classical mechanics, quantum mechanics, relativity, string theory.
- The Physics Classroom
- Free, clear high-school to early-undergrad physics explanations. Best free intro site.
- Tong — Field Theory notes
- Free Cambridge field theory lecture notes. Excellent and complete.
- Walter Lewin MIT lectures (8.01)
- The legendary MIT mechanics course. Free on OCW, still the best physics teaching ever.
- Walter Lewin MIT lectures (8.02)
- The famous 8.02 E&M series. Best electricity and magnetism explanation available.
Thermodynamics & Heat
- Absorption refrigeration
- Separates the working fluid from the refrigerant, so it can run on waste heat directly.
- Adiabatic process
- No heat transfer. Where the Poisson relations and the adiabatic lapse rate come from.
- Arovas — Thermodynamics and Statistical Mechanics
- Very thorough graduate notes, with the derivations written out rather than asserted.
- Arrow of time
- Why time has a direction in thermodynamics but not in the underlying equations.
- arXiv — chemical physics (recent)
- Recent papers on molecular thermodynamics and statistical mechanics.
- Biot number
- The test for whether a lumped capacitance model is allowed at all. Cheap check, saves a whole simulation.
- Blackbody radiation
- The reference emitter every real surface is measured against.
- Blundell — Thermal and Statistical Physics notes
- The lecture notes for the above, chapter by chapter. The fastest route through the whole subject.
- Boiling point
- Where vapour pressure reaches ambient pressure, which is why altitude matters.
- Boltzmann constant
- The bridge between microscopic mechanics and macroscopic thermodynamics.
- Boltzmann sampler
- Metropolis in one line, and the bridge from statistical mechanics to computation.
- Carnot cycle
- The most efficient possible engine, and the object the second law is really about.
- Carnot engine
- The engine itself, with its efficiency limit and how it scales with the temperature ratio.
- Carnot's theorem (thermodynamics)
- No engine between two temperatures beats a reversible one. The sharpest form of the second law.
- CFD Online
- The reference for computational fluid dynamics: theory, discretisation schemes, and a deep forum archive.
- Chemical potential
- The quantity that equalises across a system at equilibrium, and the generalisation that unifies all of the laws.
- Clapeyron equation
- The slope of a phase boundary. One line, and it gives you freezing-point depression and boiling-point rise.
- Concepts in Thermal Physics (Blundell)
- The standard undergraduate text, by the authors, with supplementary material. Free and unusually well written.
- Convection
- Advection of heat by moving fluid, and why it dwarfs conduction in liquids and gases.
- Cooling tower
- Approaching the wet-bulb limit, and what happens when you reach it.
- CoolProp (open-source property library)
- Thermophysical property data and equations of state for dozens of fluids, free and usable from code.
- Critical point (thermodynamics)
- The end of the liquid-gas boundary, and the supercritical state beyond it.
- Critical temperature
- Above it no amount of pressure liquefies the gas. The hard ceiling on any compression scheme.
- Cryogenics
- The field below about 120 K, and the materials problems that come with it.
- Dendrite (crystal)
- Why freezing is not just slow: the instability that makes freezing into fingers.
- Desiccant
- Dehumidification by adsorption rather than condensation, and why that makes it cheap below the dew point.
- Entropy (arrow of time)
- The deep end of the second law: why a low-entropy universe is a prerequisite for there being anything at all.
- Entropy (classical thermodynamics)
- The Clausius formulation and its mathematical consequences, separated from the statistical view.
- Entropy (information theory)
- Shannon entropy. The same mathematics, and the bridge to the second law of computation.
- Entropy (thermodynamics)
- The thermodynamic definition, its measurement, and the many ways it is genuinely not disorder.
- Ergodicity
- Why a closed system eventually explores its states, and when that does and does not imply equilibrium.
- Eutectic system
- The lowest possible melting point of a mixture, and why solder and ice cream are made this way.
- Evaporation
- Surface-only, below the boiling point, and the main way bodies actually cool.
- Evaporative cooler
- Works only in dry climates, and the limit is the dew point.
- Exergy
- Useful work as distinct from energy. The right way to account for inefficiency, and the basis of exergy analysis.
- First law of thermodynamics
- Energy conservation for thermodynamic systems, and why it is not by itself a law of physics.
- Fourier's law of heat conduction
- Heat flux is the negative temperature gradient times conductivity. The whole conduction model in one equation.
- Freezing
- The other side of the same transition, and the heat transfer that has to happen for it to proceed.
- Freezing point depression
- Why salt on a road and antifreeze in an engine both work, and the colligative properties behind it.
- Frost
- Deposition straight from vapour, hoarfrost windows, and the thermodynamics of ice crystals in air.
- Gibbs free energy
- Constant temperature and pressure. The reason chemistry happens in a beaker and not in space.
- Gibbs phase rule
- F = C − P + 2. Determines how many phases can coexist, and predicts the shape of every phase diagram.
- Gould & Tobochnik course materials (UMD)
- Chapters of Thermal and Statistical Physics, plus a comparison chart of the different thermodynamic derivations.
- Grashof number
- Buoyancy against viscosity for free convection, the natural-convection analogue of Reynolds.
- Heat capacity
- Specific and molar, and why water's is the reason lakes freeze from the top down.
- Heat conduction
- Diffusion of thermal energy through a medium, and the steady and transient cases.
- Heat engine
- The general class, its efficiency bound and the real thermodynamic limits on work extraction.
- Heat pump
- Moves heat rather than generating it, so the efficiency figure can exceed one. Thermodynamically correct and often misunderstood.
- Heat transfer
- Conduction, convection and radiation, and which one dominates where.
- Helmholtz free energy
- Constant temperature and volume. The natural potential for statistical mechanics and for rate constants.
- IAPWS
- The industrial formulations for water and steam, including the IF97 standard. The reference for anyone doing water thermodynamics.
- Ice
- Every known phase, why the ordinary one is so unusual, and the hydrogen bond that explains it.
- Isobaric process
- Constant pressure. Where enthalpy, the specific heat of air and most steady-flow engineering come from.
- Isochoric process
- Constant volume. Rigid container heating, and the simplest path for measuring heat capacity.
- Isothermal process
- Constant temperature. Ideal gas at constant T, and reversible expansion in general.
- Kelvin
- The absolute scale, and the work behind the second law as a statement about impossibility.
- Kirchhoff's law of thermal radiation
- A good absorber is a good emitter, wavelength by wavelength. The bridge between absorption and emission.
- Latent heat
- Energy that changes phase without changing temperature, and the reason freezing releases rather than absorbs it.
- Laws of thermodynamics
- All four laws on one page, with the history of how each was arrived at. The best single starting point.
- Maxwell–Boltzmann distribution
- The equilibrium distribution, and the result the whole subject is built to explain.
- Melting
- The transition itself, with nucleation and the difference from a first-order transition in general.
- Melting point
- What actually determines it, and why pressure moves it for water but not for most substances.
- MIT OCW 2.051 — Introduction to Heat Transfer
- The first course in the sequence, with exams and full problem sets.
- MIT OCW 2.51 — Intermediate Heat and Mass Transfer
- Lienhard's heat transfer text as a course, including radiation, condensation and boiling.
- MIT OCW 8.333 — Statistical Mechanics I
- Kardar's course, opening with four lectures straight on the laws of thermodynamics, plus full video.
- MIT OCW 8.334 — Statistical Mechanics II
- The sequel: universality, correlation functions, scaling and the renormalisation approach to phase transitions.
- Nair — Thermodynamics and Statistical Mechanics (LibreTexts)
- A complete free text that derives the laws one at a time, including the Caratheodory formulation.
- Newton's law of cooling
- Rate proportional to temperature difference. The basis of every lumped-capacitance calculation.
- NIST WebBook — fluid properties
- Thermophysical property data for pure fluids and mixtures, straight from NIST.
- NPTEL
- Free Indian lecture series across engineering and science, with full video for most courses.
- Nucleation
- How a phase change actually starts. The barrier that makes freezing, boiling and crystallisation finite-rate.
- Nusselt number
- Conductive to convective transport at a surface. The correlation you look up for any convection problem.
- Partition function (statistical mechanics)
- The single object from which every equilibrium quantity is derived. Worth understanding properly.
- Phase transition
- First and second order, critical exponents, and why water is the awkward one.
- Phase-change material
- Storing heat in the latent heat of a phase change, and why that is worth far more than sensible heat.
- Prandtl number
- Momentum diffusivity against thermal diffusivity. Which boundary layer wins, thick or thin.
- Radiative transfer
- Emission, absorption, scattering and the radiative transfer equation.
- Rayleigh number
- Buoyancy against viscous and thermal diffusion. Sets whether free convection happens at all.
- Recrystallization (metallurgy)
- Cold work, stored energy, heat, and new grains. Solid-state phase change at industrial scale.
- Refrigeration
- The full picture, including the Carnot limit and why a fridge with a 10 K temperature difference is efficient.
- Reversible process
- The idealisation the second law is about, and the reason entropy generation is the measure of irreversibility.
- Schroeder-based thermal physics notes (SMU)
- A semester of links and notes built around Schroeder's textbook, good for topic-by-topic study.
- Sean Carroll — Statistical Physics notes
- Carroll's full graduate notes, free, with the informal explanations the textbooks leave out.
- Second law of thermodynamics
- Entropy always increases. Also carries the Kelvin-Planck and Clausius statements, which is where most people meet them.
- Sethna — Statistical Mechanics
- Entropy, order parameters and complexity. Free full text, and exceptionally good on phase transitions.
- Sherwood number
- The mass-transfer analogue of the Nusselt number, for diffusion-driven transport.
- Specific heat capacity
- Per-unit-mass values and tables. The number you need for nearly every heat transfer calculation.
- State function
- Path independence, exact differentials, and why heat and work are not state functions.
- Statistical mechanics
- How the macroscopic laws are derived from the microscopic ones. The companion to the laws themselves.
- Stefan problem
- The moving-boundary problem of a solid melting or a liquid freezing. The classic coupling of heat conduction to phase change.
- Stefan–Boltzmann law
- Total radiated power goes as the fourth power of temperature. Why small absolute temperatures matter enormously.
- Stirling engine
- An external combustion engine that can approach the Carnot limit. Regeneration is the interesting part.
- Styer — Statistical Mechanics
- A free modern text that treats thermodynamics as a deduction from entropy existing. Rigorous and readable.
- Sublimation (phase transition)
- Solid straight to gas, and why freeze-drying works because of it.
- Supercooling
- Liquid below its freezing point, and why it needs a nucleation site to snap solid.
- Thermal conductivity
- The material property, its temperature dependence, and why diamond and aerogel bracket the range.
- Thermal diffusivity
- Conductivity over volumetric heat capacity. The number that actually says how fast something heats up.
- Thermodynamic equilibrium
- Thermal, mechanical and chemical equilibrium together, and the state functions they force to be constant.
- Thermodynamic temperature
- Temperature defined by the second law rather than by an expansion of mercury. The deep reason for the Kelvin scale.
- Third law of thermodynamics
- The unattainability of absolute zero, and why it settles that entropy has a definite value.
- Triple point
- Where all three phases coexist. Not a curiosity: it fixes the point where the whole diagram degenerates.
- Vapor pressure
- The equilibrium quantity behind evaporation, boiling, drying and distillation alike.
- Vapor-compression refrigeration
- The cycle almost every refrigerator and air conditioner actually runs.
- View factor
- The fraction of radiation leaving one surface that reaches another. Geometry without which radiation nets do not close.
- Waste heat
- Where it goes, how much is recoverable, and why data centres are now a heat source rather than just a load.
- Zeroth law of thermodynamics
- Why temperature is even definable, and why it had to come first.
Electronics, Robotics & Devices
Circuits & Signals
- 3Blue1Brown — Fourier transform
- Free visual introduction to the Fourier series and transform. Brilliant.
- All About Circuits — filters and op-amps
- Free chapters on op-amps, active filters and oscillators. Excellent.
- All About Circuits — worksheets
- Free problem worksheets for every electronics topic. Great for practice.
- Analog Devices — signal chain tutorials
- Free application notes on op-amps, filters, ADCs and every signal-chain block.
- Control.com — free resources
- Free control engineering news and technical articles. Good industry signal.
- Convex Optimization (free PDF)
- Boyd & Vandenberghe's textbook, free online. The standard reference.
- Coursera — Digital Signal Processing
- Free audit track from a strong programme. Practical DSP with MATLAB.
- Deep Learning — the book (free)
- Goodfellow, Bengio & Courville's textbook, free to read online. Exceptional.
- DSP Stack Exchange
- Best free Q&A for signal processing theory and implementation.
- Free DSP — DSP Stack Exchange wiki
- Free deep Q&A on Fourier analysis and filtering. Browseable by tag.
- Gilbert Strang — full lectures
- Strang's free linear algebra course. The best explanation of Fourier there is.
- GNU Radio — DSP blocks
- Free documentation for real-time SDR and DSP flowgraphs. Excellent.
- Mathematics for Machine Learning (free PDF)
- Deisenroth et al. Free complete book on the maths behind ML. Very good.
- MIT 6.003 — Signals and Systems
- Gilbert Strang's free MIT course. The definitive intro to Fourier and filtering.
- MIT 6.341 — Discrete-Time Signal Processing
- Free MIT graduate course on DSP. Rigorous and complete.
- MIT OCW — electronics & circuits search
- Browse every free MIT electronics and circuits course.
- PySDR
- Free textbook on software-defined radio. Extremely well written and complete.
- Scilab — signal processing toolbox
- Free open-source numerical computing with signal processing functions.
- Scilab / Octave for signal work
- Free open-source MATLAB alternative. Perfect for filters and control work.
- The Elements of Statistical Learning (free)
- Hastie, Tibshirani & Friedman. Free PDF, the classic ML reference.
- The Scientist and Engineer's Guide to DSP
- The single best free book on digital signal processing. Complete, online, superb.
- Understanding Machine Learning (free PDF)
- Mohri et al. Free complete theoretical ML textbook PDF.
Computer Architecture
- Arm — Cortex-M processors
- Free official ARM architecture manuals and reference docs.
- Branch prediction explained
- Free detailed article on modern branch predictors. Good CS reading.
- C4 model — software architecture
- Free notation for describing software architecture. Very clear and useful.
- comp.lang.riscv newsgroup
- Free RISC-V mailing list archives. Real design discussion.
- Compute Shader Home
- Free browser GPU shader playground. Great for learning parallel graphics.
- CPU cache — Wikipedia overview
- A free, well-referenced overview of cache design. Good starting point.
- Google Cloud TPU docs (free)
- Free architecture documentation for Google's tensor processing units.
- GPU Gems (free online)
- The classic free GPU programming book, chapters online. Timeless techniques.
- GPUOpen — AMD developer resources
- Free compute and graphics optimisation guides from AMD. Very practical.
- MIT 6.004 — Computation Structures
- Free MIT course on how digital hardware becomes a working computer.
- Modern Hardware — Chipworks
- Free encyclopedia of CPU microarchitectures. Reference for x86 and ARM internals.
- OpenGL tutorial (learnopengl)
- Free, well-written OpenGL tutorials. Still the best graphics intro.
- OpenPOWER ISA
- Free documentation for the open Power ISA architecture.
- Ray Tracing in One Weekend
- Free ray tracing book series, three volumes. Beautiful and complete.
- Real-Time Rendering (free online)
- Apress's rendering textbook, free to read online. The best graphics reference.
- ROCm documentation (free)
- Free open-source GPU compute stack docs from AMD. Very solid.
- Structurizr (free tier)
- Free tool for C4 architecture diagrams as code. Excellent for design docs.
- The Elements of Computing Systems
- Nisan and Schocken's full textbook, free to read. Hardware meets software.
- Virtual memory and paging
- Free detailed article on paging, TLB and page tables. Very good.
- Vulkan tutorial (free)
- Free step-by-step Vulkan tutorials. The best way into modern graphics.
- WebAssembly spec (free)
- The free WebAssembly specification. Read it for a clean design view.
- WebGL fundamentals
- Free excellent WebGL course. Best entry to GPU programming for the web.
- WebGPU explainer (free)
- Free official WebGPU specification. The modern graphics API for the web.
Device Repair
- Advanced Electronics Repair forum
- Free deep troubleshooting knowledge base. The place for hard faults.
- Battery University (free)
- Free excellent technical articles on batteries, charging and power. Outstanding.
- Electronics Repair School forum
- Free practical electronics repair advice and diagnostic threads.
- Electronics Stack Exchange — repair
- Free Q&A on diagnosing and fixing broken electronics. Excellent.
- Hackaday — repair and teardowns
- Free teardowns of everything, with analysis of what the makers did.
- iFixit — all devices
- Free repair guides, exploded views and teardowns for thousands of devices.
- iFixit — game console repair
- Free console repair guides with teardowns. Excellent for learning.
- iFixit — smartphone repair
- Free phone repair guides, from screen to charging port.
- iFixit — tools & supplies
- Free tool guides: which screwdriver, what tweezers, how to use them.
- Multimeter basics — All About Circuits
- Free chapters on measurement, meters and instrument basics. Essential.
- Reddit — r/mobilerepair
- Free community for phone and device repair questions. Good photos.
- Right to Repair (iFixit)
- Free background on the right-to-repair movement and why it matters.
- Sigrok — protocol decoding
- Free open-source decoders: I2C, SPI, UART, USB. Powerful for debugging.
Electricity & Power
- All About Circuits — AC theory
- Free chapters on AC, phasors, reactance and resonance. Clear and rigorous.
- Climate Action Tracker
- Free independent tracking of national climate pledges. Data-rich.
- Coursera — Electric Power Systems
- Free audit track on grid fundamentals and operation.
- DOE — Energy Saver
- Free practical guides on household energy use and efficiency.
- Electricity — The Engineering Mindset
- Free clear explanations of three-phase, transformers and substations. Excellent.
- Electricity Prices and Bills (US)
- Free official data on electricity prices, generation and retail markets.
- Ember — electricity data explorer
- Free open data and analysis on the global electricity transition. Excellent.
- Ember — free data downloads
- Free downloadable global electricity datasets with clear methodology.
- ENTSO-E Transparency Platform
- Free European grid data: load, generation, prices, congestion. Superb.
- Eurostat — energy
- Free official European energy statistics, well documented.
- Grid — National Renewable Energy Lab
- Free research on grid integration of renewables. Modern and relevant.
- IEA — energy data
- Free international energy statistics and reports. Authoritative.
- IEEE — power & energy
- The IEEE Power & Energy Society. Free tutorials, standards info and events.
- IPCC reports
- Free authoritative climate reports, with the underlying data. Essential.
- J. P. Holman — Heat Transfer
- Free MIT heat transfer and thermodynamics course materials.
- NREL — renewable energy research
- US National Renewable Energy Laboratory. Free datasets, tools and reports.
- Open Power System Data
- Free, openly licensed power system data for Europe and beyond. Genuinely useful.
- Our World in Data — energy
- The best free charts on energy production, use and emissions worldwide.
- Power to the People
- Free data-driven explanation of renewable energy growth. Excellent.
- Renewables — IEA Renewables
- Free IEA data and analysis on global renewable capacity.
- The Engineering Mindset
- Free electrical engineering blog and YouTube channel. Outstanding power explanations.
- UNECE — energy statistics
- Free official energy statistics database for many countries.
- US EIA — energy data
- Free official US energy statistics, electricity data and forecasts.
- World Nuclear — nuclear power data
- Free global nuclear power statistics and reactor information.
Electronics
- Adafruit Learning System
- Free, well-written tutorials on every component and project. The best practical resource.
- All About Circuits — textbook
- The classic free online electronics textbook. DC, AC, semiconductors, digital. Essential.
- CERN — open hardware
- The Open Hardware Repository: free, open hardware designs and CERN's own.
- CircuitLab — online schematic simulator
- Free tier browser schematic capture and simulation. No install needed.
- Digi-Key — tech resources
- Free component data, application notes and design guides from a major distributor.
- DigiKey — component selection guides
- Free maker projects with full BOMs, useful for real designs.
- EDN — engineering design news
- Free electronics industry news, design tips and analysis.
- EEVblog
- Dave Jones' free electronics engineering videos and forum. Brilliant teaching.
- EEVblog — YouTube
- Free teardowns, lab tours and design reviews. Very entertaining and useful.
- Electronics Stack Exchange
- The best free Q&A for electronics design and theory. Search before asking.
- Electronics-Tutorials.ws
- Free, well-organised electronics tutorials covering theory and components.
- Embedded.fm podcast
- Free weekly podcast about embedded systems development. Very high quality.
- EveryCircuit
- Free interactive circuit simulator with a real-time scope. Great for intuition.
- Falstad — logic & digital sims
- Free browser simulators for circuits, logic, physics and more. Instant and free.
- Falstad Circuit Simulator
- Free, tiny, instant circuit simulator in the browser. Brilliant for learning.
- GNU Radio
- Free open-source software radio. Real DSP on real signals. Outstanding project.
- Hackaday
- Free hardware hacking news and projects. The best hardware blog on the web.
- Horowitz & Hill — The Art of Electronics companion
- Free student resources and worked examples from the authors of The Art of Electronics.
- KiCad
- Free, open-source professional PCB CAD suite. Schematics, layout, 3D. The standard.
- KiCad — getting started
- Free official documentation and tutorials for the whole PCB toolchain.
- KiCad — open source EDA
- Why KiCad is a serious professional alternative. Free and open source.
- LCSC — components
- Free component catalogue with datasheets and photos. Good for BOM work.
- Make: Electronics
- Free projects and tutorials from the Make magazine team. Hands-on and fun.
- MIT 6.002 — Circuits and Electronics
- The free MIT intro course that made analog electronics click. Full lecture videos.
- Mouser — design resources
- Free application notes, whitepapers and reference designs.
- ngspice
- Free open-source SPICE circuit simulator. The industry-standard open simulator.
- Nuts and Volts magazine
- Free electronics magazine with a large PDF archive. Very useful.
- Open Source Hardware Guide
- Free guide to what open source hardware means and how to do it.
- OSHWA — Open Source Hardware
- The Open Source Hardware Association. Free definition and licensing of hardware.
- Planet Analog
- Free analog design news, columns and tutorials. Well edited.
- PulseView (sigrok GUI)
- Free open-source GUI for logic analysers. Works with cheap hardware. Excellent.
- Reddit — r/AskElectronics
- Beginner-friendly electronics help. Good for learning the right questions.
- Reddit — r/electronics
- Active community for electronics design questions and projects.
- Sigrok
- Free open-source logic analyser / protocol decoder software. Use with a cheap analyser.
- Silicon Engineering Stack Exchange
- Best free Q&A for semiconductor device physics and fab topics.
- SparkFun Tutorials
- Free tutorials with clear schematics and code. Excellent first stop for beginners.
- Texas Instruments — The Analog Experience
- Free textbook and online training from TI. Plus datasheets and reference designs.
- The Amp Hour (podcast)
- Free weekly electronics engineering podcast. Interviews and deep dives.
- Tinkercad Circuits
- Free browser-based circuit simulator with Arduino. Perfect for absolute beginners.
Embedded & Devices
- Arduino documentation
- The official free Arduino language and board reference. Start here.
- Arduino Project Hub
- Free community projects, most beginner friendly. Great for starting.
- BlueZ (Linux Bluetooth)
- Free open-source Bluetooth stack for Linux. Official protocol docs.
- CircuitPython
- Free Python for Adafruit boards. Beginner friendly, huge library set.
- DigiKey — microcontroller resources
- Free maker projects and design resources. Practical and well documented.
- ESP-IDF documentation
- Free official ESP32 SDK documentation. Very thorough.
- FreeRTOS
- The most popular free open-source RTOS kernel. Free docs and downloads.
- Hackster.io
- Free community projects for hardware and IoT. Good inspiration.
- Interrupt Journal
- Free online magazine about embedded systems. Well written and practical.
- MicroPython
- Free Python for microcontrollers. Open source, and a joy to use.
- Nerves (Elixir embedded)
- Free open-source embedded framework using Elixir. Elegant approach.
- Nordic Developer Academy
- Free nRF training courses and video lectures. Very good quality.
- Nordic nRF Connect for Desktop
- Free tool for programming and debugging Nordic BLE chips.
- PlatformIO
- Free open-source toolchain and library manager for embedded. Saves hours.
- Raspberry Pi documentation
- The official free Pi documentation. Extensive and well written.
- Raspberry Pi Pico SDK
- Free SDK for the RP2040/Pico microcontroller. Excellent C/C++ docs.
- RP2040 datasheet
- The free official RP2040 datasheet. Exceptionally well written for a datasheet.
- Sensor interfaces (SparkFun guides)
- Free practical guides on wiring and reading every common sensor type.
- STM32CubeIDE
- Free ST IDE for ARM microcontrollers, with HAL and examples.
- TinyUSB
- Free open-source USB stack for embedded. Extremely useful and well documented.
- Zephyr getting started
- Free guides to set up Zephyr and build for boards. Very good.
- Zephyr RTOS
- Free open-source real-time OS with excellent docs. A modern standard.
Hardware & Making
- Advanced Electronics Repair
- Free forum and knowledge base for complex electronics repair. Very knowledgeable.
- BOM — parts search
- Free electronic component search with datasheets and pricing. Essential.
- Buildroot
- Free open-source embedded Linux build system. Simpler than Yocto.
- ChargerLAB
- Free teardown site for chargers, power banks and batteries. Excellent photos.
- CNX Software
- Free embedded and open-source hardware news site. Very active.
- Debian — embedded images
- Free guidance on running Debian on embedded devices.
- Device Tree Specification (free)
- The free Device Tree specification for describing hardware on Linux.
- Electronics Repair School
- Free electronics repair forum with excellent practical troubleshooting threads.
- Engineering ToolBox (calculators)
- Free engineering calculators and reference tables. Genuinely useful.
- FreeCAD
- Free open-source parametric CAD. A full mechanical design suite.
- Fusion 360 personal use
- Free for personal and educational use. Excellent integrated CAD/CAM.
- Google Tech Dev Guide — hardware
- Free developer guides, including hardware and Android device topics.
- GrabCAD — free models
- Free CAD model library. Useful for parts and references.
- Hackaday.io — project logs
- Free project write-ups with schematics and code. Excellent learning material.
- iFixit — Electronics repair
- Free electronics repair guides, soldering and troubleshooting. Very useful.
- iFixit — free repair guides
- Free step-by-step repair guides for almost every device ever made. Exceptional.
- Inkscape
- Free open-source vector graphics. Standard for panel design and silkscreen.
- JLCPCB assembly service
- Affordable PCB fabrication and assembly, widely used for prototypes.
- Kicad footprint libraries
- Free open-source PCB footprint libraries. Part of the KiCad ecosystem.
- Linux on embedded devices
- Free Linux kernel documentation, including embedded and device trees.
- Louis Rossmann
- Free detailed repair videos (microscope soldering, board level). Outstanding.
- NASA Spinoff
- Free examples of real technology transfers and engineering solutions. Good reading.
- Onshape — free CAD (education)
- Free browser CAD with a free educational licence. Professional quality.
- Open Source Telescope (OST)
- The world's first fully open source telescope. Amazing free hardware design.
- OpenSCAD
- Free open-source parametric CAD for 3D models. Excellent for parts.
- PCBWay — prototyping
- Affordable PCB and 3D printing for prototypes and small runs.
- Prusa Knowledge Base
- Free 3D printing documentation and troubleshooting. The best printer docs.
- Prusa Printables
- Free library of printable 3D models. Great source of parts.
- SnapEDA — free components
- Free component symbols and footprints for KiCad and Altium. Very helpful.
- Yocto Project
- Free open-source Linux build system for embedded devices. Excellent docs.
Robotics & Control
- ArduPilot documentation (free)
- Free developer docs for ArduPilot, the open drone autopilot.
- Caltech CDS — control systems
- Free control systems course notes with MATLAB and Python exercises.
- Free control theory references (MIT OCW)
- Free MIT control systems course materials. Browse the whole list.
- Gazebo simulator documentation
- Free docs for the Gazebo robot simulator.
- Kalman and Bayesian Filters in Python
- A free book as a Jupyter notebook. The clearest Kalman filter tutorial.
- KITTI Vision Benchmark (free)
- The free classic dataset for driving vision research.
- Modern Robotics (free course)
- A free Coursera course from Northwestern covering grasping, planning and control.
- nuScenes dataset (free)
- A free, large-scale autonomous driving dataset from Boston and Singapore.
- Open Robotics Middleware: ROS index
- Free site for ROS ecosystem, distributions and community.
- OpenAI Gym / Gymnasium docs
- Free reinforcement learning environment docs. The standard for RL research.
- OpenCV documentation (free)
- The free official OpenCV docs. Computer vision for everyone.
- Oxford RobotCar dataset (free)
- A free large-scale urban driving dataset from Oxford.
- Probabilistic Robotics (Thrun, free PDF)
- The definitive SLAM textbook, free official PDFs per chapter. Landmark.
- PX4 autopilot documentation
- Free docs for the PX4 open-source drone autopilot. Very well written.
- ROS 2 documentation (free)
- The free official ROS 2 docs. The standard robotics framework.
- SLAM for Dummies (free)
- A free, gentle introduction to SLAM. Perfect if the math is intimidating.
- State Estimation for Robotics (Barfoot, free)
- A free, rigorous book on Bayesian state estimation and SLAM. Outstanding.
- Underactuated Robotics (MIT, free book)
- A free, excellent MIT textbook on nonlinear control and legged robots.
Semiconductors & Chips
- ASML — how lithography works
- Free excellent explanation of lithography, the core of chip making.
- Ben Eater — 8-bit computer
- Free video series building a working computer on breadboards. Absolutely superb.
- Chipyard
- Free open-source RISC-V SoC generator in Chisel. Great for learning CPU design.
- Chisel — hardware DSL
- Free hardware construction language from Berkeley. Modern and learnable.
- Efabless
- Free tools and programs for open source chip design. Very community driven.
- IEEE IRDS — device roadmap
- The free International Roadmap for Devices and Systems. Free detailed reports.
- IEEE Spectrum — semiconductors
- Free chip industry coverage: process nodes, fabs, packaging, geopolitics.
- imec — semiconductor research
- Free overview of advanced semiconductor research and process technology.
- Ken Shirriff's blog
- Free deep reverse-engineering of chips, CPUs, keyboards and transistors. Legendary.
- Nand2Tetris
- Free course: build a computer from NAND gates in software, then in hardware.
- NPTEL — free courses (VLSI)
- Free Indian government university courses, including excellent VLSI and semiconductor ones.
- OpenLane
- Free open-source silicon design flow built on OpenROAD. Runnable end to end.
- OpenPDK
- Free open Process Design Kits maintained by Efabless and partners.
- OpenROAD project
- Free open-source RTL-to-GDSII flow for ASIC design. Real tools, free.
- Princeton — Koselija? transistor history
- Free Silicon Engine history of semiconductor technology. Illustrated and deep.
- RISC-V International
- The open ISA standard body. Free specs, education and ecosystem news.
- Semiconductor Engineering
- Free industry news on chip design, fabs and packaging. Very good reporting.
- SemiWiki
- Free semiconductor industry analysis and news, with a strong engineering voice.
- SkyWater PDK (open)
- Free, open Process Design Kit for silicon. Enables real chip simulation.
- The Chip Letter
- Free newsletter on chiplets and advanced packaging. Very current.
- Tiny Tapeout
- Free, learn chip design by actually fabbing a tiny chip. Remarkable project.
- Verilator / Icarus Verilog
- Free open-source Verilog simulators. Write and simulate HDL for free.
- VLSI Academy
- Free VLSI design tutorials and interview material. Practical and clear.
- What Every Programmer Should Know About Floating-Point
- Free classic explanation of floating point arithmetic. A must-read.
- What Every Programmer Should Know About Memory
- Free classic paper on how memory, caches and the stack actually work. Essential.
- Wikichip
- Free encyclopedic database of CPUs, GPUs and their internals. Superb reference.
- Wokwi — online simulator
- Free browser-based electronics and Arduino/ESP32 simulator with real library support.
English: Grammar, Vocabulary & Writing
English Dictionaries & Corpora
- BYU English corpora
- Corpora with a user interface and the ability to search them without downloading. Extremely useful.
- Comparative linguistics
- How languages are compared to reconstruct lost ones. The source of most etymology work.
- Computational linguistics
- The field, its methods, and the free tools. Good orientation for anyone working with text data.
- Corpus linguistics
- What corpora are and the kinds of conclusions they license. The method behind every modern dictionary.
- Dialect
- How varieties arise from a single language, and why 'correct' is a political claim.
- English-Corpora.org
- Large freely downloadable text corpora with frequency lists. The best raw data for vocabulary work.
- Grimm's law
- The consonant shift behind all Indo-European vocabulary. The concrete reason English words are odd.
- Historical linguistics
- How languages change over centuries, and why it is regular enough to study.
- Language change
- Why every language is always in motion, and how we can measure it.
- Language death
- What happens when a language stops being spoken, and what it costs. Also English, historically.
- Morpheme
- The smallest meaning-bearing unit, and how to spot one in a real word.
- Morphology (linguistics)
- How words are built from smaller pieces. Where English affixation is systematic and where it is not.
- Natural language processing
- The field overview. Relevant if you are building anything that reads English text.
- Oxford English Dictionary
- The definitive historical dictionary. Free word-by-word access; subscription for full use. Where etymology is settled.
- Sociolinguistics
- Language as a social fact: who speaks what to whom, and with what consequence.
English Exercises & Practice
- Babbel
- Short focused lessons, well designed but largely paid. Worth a trial if you want structure.
- Busuu
- Structured courses with real human feedback on your writing. Good for the feedback loop.
- Duolingo
- Gamified practice. Weak on explicit grammar, good for maintaining daily contact with the language.
- Ellii — English teaching blog
- A long-running English teaching site with free printable materials, games and teaching advice.
- English Lessons
- Free lessons and quizzes across levels, with a strong focus on everyday functional English.
- EnglishClub
- Structured lessons with exercises on every topic, from tenses to business English. Long-established and free.
- Genius — annotated lyrics
- Lyrics with user annotations explaining slang and vocabulary in context. An unusually rich source of real usage.
- Lyrics.com
- Lyrics for dictation practice, and for checking how a phrase is actually used in a song.
- Memrise
- Spaced repetition with real-video clips, which is much better for listening than flashcards.
- Perfect English Grammar
- Granular grammar exercises, each one isolated to a single point. Ideal for targeted drilling of a specific problem.
- Quizlet
- User-made flashcard sets for almost any textbook or exam. Useful for drilling a syllabus you already have.
- Rocket English
- Drills that push active recall rather than passive reading. Free tier is usable.
- setlist.fm
- Setlists for live performances. Free dictation material with real singers and real audiences.
- Storynory
- Free graded audio stories with transcripts. Good listening practice for intermediate and above.
- UsingEnglish
- Free exercises on every grammar point plus vocabulary and writing practice. The largest bank of usable drills in English.
- WordReference forums
- Ask and answer threads on word choice, register and idiom. Reading others' questions is itself good practice.
English for Academic Purposes
- Academic English (EAP) materials
- Cambridge's EAP resources and the exam definitions. The official specification of the target.
- American English
- The US State Department's free teaching materials and podcasts. Far more useful than the name suggests.
- Basic English
- Ogden's controlled 850-word vocabulary. Fascinating and genuinely useful for clear writing.
- Cambridge English exams
- B2 First and C1 Advanced, the exams most institutions actually ask for. Free sample papers.
- English as a second or foreign language
- The field, its history, and the distinction between ESL and EFL that shapes how it is taught.
- English for everyone (Coursera)
- Academic English specialisations from top universities. Audit is free.
- Falsification
- How a claim is shown to be wrong, and why you cannot verify your own argument. Relevant to persuasive writing.
- IELTS
- The Academic and General Training modules, with free practice tests. The most widely recognised academic English test.
- International English
- Which Englishes are taught, and the argument about whether one should be privileged.
- Language acquisition
- Child and second-language acquisition compared, and what the differences mean.
- Lingua franca
- Why English became the academic lingua franca and what that does to how we write.
- National Council of Teachers of English
- Research-backed standards and free position statements on English teaching. The primary literature.
- Pearson PTE Academic
- A computer-delivered academic English test with free practice and detailed scoring guides.
- Second-language acquisition
- The research field behind how languages are actually learned. The theory most teachers never read.
- TES — teaching resources
- A very large library of free classroom materials, lesson plans and course documents.
- TESOL International
- The professional body for English language teaching, with free standards and position statements.
- TOEFL
- The North American academic English test, and its free practice material.
English Grammar
- Active voice
- The default, and the easier one to master. Worth internalising before touching the passive.
- Adjective
- Attributive versus predicative use, and the order that adjectives appear in.
- Adposition
- Prepositions and postpositions, and the fact that English words them prepositions out of oddity.
- Adverb
- Manner, place, time, degree, and why 'very' only modifies a few of them.
- Anglo-Link — grammar posts
- A well-established site on tricky grammar and idiom, with a blog that regularly nails the details.
- Auxiliary verb
- Do, have and be in their auxiliary forms, and why English builds so much with them.
- Cambridge Dictionary grammar reference
- The clearest free grammar reference by category: tenses, articles, word classes, punctuation. Start here.
- Clause
- The unit that grammar is actually built from. The single most useful structural concept in English.
- Cleft sentence
- It was John who said it. A way to put any element into focus, and a staple of spoken English.
- Conjunction (grammar)
- Coordinating, subordinating and correlative, with the parallel structure each requires.
- Copula (linguistics)
- 'Be' is not just to be. The copula system English actually uses, including 'remain' and 'seem'.
- Determiner
- The article, demonstrative, possessive and quantifier system in one place.
- English grammar (overview)
- The systematic description of English grammar, with the terminology every other resource assumes.
- English Grammar Usage Lab
- Barry's free grammar site: dense, precise explanations of the rules people actually get wrong.
- Existential clause
- There is, there are and their unpredictable verb agreement. A persistent learner trap.
- Gerund
- The -ing form, and the long list of verbs that accept one and not the other. Pure memorisation.
- Grammar (overview)
- What grammar is and the schools of thought about it. Useful context for why rules differ between books.
- Grammar Book (Wiley)
- Large plain-language grammar explanations, with a useful diagnostic index for finding your specific problem.
- Grammar slideshow index
- The full index of Randall's grammar lessons. A good map of what to study in what order.
- Grammatical aspect
- The distinction that trips up speakers of Romance and Slavic languages: how completed and ongoing action is marked.
- Grammatical case
- The objective case survives in English only as 'me' and 'whom'. Everything else is vestigial.
- Grammatical mood
- Indicative, subjunctive, imperative and the places English still uses the subjunctive.
- Imperative mood
- Commands, warnings and the 'do not' negative form that confuses learners.
- Infinitive
- The bare and 'to' infinitive, and the verbs that take one but not the other.
- Modal verb
- Can, could, may, might, must, shall, should, will, would. The most heavily overloaded part of English.
- Noun phrase
- What counts as a noun phrase, and why the boundaries surprise people.
- Participle
- Present and past participles, reduced relatives, and the dangling-participle error.
- Passive voice
- How it forms, when it is genuinely better, and when it is just a bad habit.
- Predicate (grammar)
- The other half of the clause, and the two forms it can take.
- Randall's ESL Grammar Lab
- Well-organised grammar and pronunciation lessons with quizzes, freely usable by teachers and self-learners.
- Rock your grammar
- Clear grammar explanations with audio, organised by point rather than by level.
- Subject (grammar)
- How the subject is identified, and the cases where it is missing or deferred.
- Subjunctive mood
- Where English still requires it, and why it survives in only a handful of fixed expressions.
- Syntax
- How words are ordered into meaning, and the three levels of structure every language has.
- Tense (grammar)
- The tense system of English in one article: how it maps onto time and how it does not.
- Topicalization
- Moving an element to the front for emphasis, and what that costs you grammatically.
- Verb
- Main verbs, auxiliary behaviour, and the irregular forms that must simply be memorised.
- Word order
- Subject-Verb-Object and its rigid consequences: why 'a car crashed into' is a fragment.
English Linguistics Research
- Chomsky hierarchy
- The four language classes and why they matter for parsing and formal syntax.
- Creole language
- What happens to a pidgin when it becomes a first language, and what it implies about innate structure.
- Dependency grammar
- The main alternative to constituency analysis, and better at free word order languages.
- Esperanto
- The most successful constructed language, and a working test case for linguistic universals.
- Functional grammar
- Language as resource for making meaning, rather as system of forms. Very accessible.
- Generative grammar
- Chomsky's programme, its claims, and the long-running debate about what it should mean.
- Head (linguistics)
- The head of a phrase, and why determining it is the central problem in phrase structure.
- International auxiliary language
- Constructed languages, and the design arguments between them. Free dictionaries exist for all.
- Linguistic relativity
- Does language shape thought? The strongest version of the claim, and the evidence.
- Minimalist program
- The current version of generative theory. Hard going, but the place the field went.
- Phrase structure grammar
- The first serious syntactic formalism, and the intuitions it was built to capture.
- Pidgin
- How contact languages arise, and why English is largely a pidgin already.
- Simlish
- The constructed language from The Simpsons, and the real work behind it. Genuinely rigorous.
- Transformational grammar
- Generative grammar's actual method, and how it grew out of grammatical transformation experiments.
- X-bar theory
- The notation that made constituent structure visible. Still the clearest introduction to syntax.
English Pronunciation & Listening
- BBC Learning English
- Free courses, audio and video, with an English We Speak series on natural delivery. Excellent and free.
- Breaking News English
- Free lesson material built around real news audio, at graded levels, with printables.
- Diphthong
- The eight English vowel movements from one position to another. Essential for the cot-caught merger.
- EngVid — English video lessons
- Short video lessons on English vocabulary and pronunciation, free, with native speakers.
- General American English
- The American standard, and how it differs from RP in the ways that matter for learners.
- International Phonetic Alphabet
- Every symbol, with examples and audio. Learn this and dictionary transcriptions stop being mysterious.
- International Phonetic Association
- The official IPA charts and the record of the alphabet itself. The reference for pronunciation.
- Intonation (linguistics)
- Pitch movement, the difference between a question and a statement, and meaning in the melody.
- Lingualeo
- Pronunciation feedback with a speech-recognition engine. Free tier, and useful for shadowing.
- Minimal pair
- The technique for training the ear, and the reason some pairs are hard for native speakers too.
- Phoneme
- The smallest sound that can change meaning, and why 'phoneme' is not a physical sound.
- Phonetics
- The physical side of speech, and how speech sounds are actually produced. Corrects a lot of intuition.
- Phonology
- How a language organizes sound into meaning, as opposed to just producing it. The more useful half.
- Prosody (linguistics)
- Stress, rhythm, intonation and pauses together. Where most of natural delivery lives.
- Received Pronunciation
- Standard British English. The reference accent, and now one of several.
- Stress (linguistics)
- Nucleus versus stress, sentence stress, and where English puts the emphasis in a phrase.
- Syllable
- Syllable structure, stress patterns, and how English word stress actually works.
- TalkEnglish
- Audio lessons for business English, mostly free, with a clear progression.
- TED Talks
- The best free material for authentic accent and pace. Use transcripts alongside.
English Vocabulary & Phrases
- Cambridge Dictionary
- Very clear definitions in learner-friendly language, with British and American pronunciations.
- Dictionary.com
- A general dictionary plus a good thesaurus. Useful for finding the word you half remember.
- English phrasal verbs
- The phrasal verb system in one article, including separable and inseparable ones. The trickiest area for learners.
- Eponym
- Words named after people, and why that is such a productive way for languages to grow.
- False cognate
- Words that look like translations and are not. A classic trap for Spanish and Portuguese speakers.
- Forvo pronunciation database
- User-submitted pronunciations in many languages. A safety net for regional and rare words.
- Heaps's law
- Predicting vocabulary growth from text length. The counterpart to Zipf for learners.
- Idiom
- Why idioms are not decomposable, and how idiomaticity differs from figurative meaning.
- Interleaving
- Mixing topics feels worse and works better. Counterintuitive and well demonstrated.
- Lexeme
- The vocabulary-learning unit: one sense, one pronunciation, regardless of grammatical variation. Worth understanding before you study.
- Longman Dictionary of Contemporary English
- The free online edition. Its audio pronunciation and 'collins' feature make it uniquely good for speaking.
- Merriam-Webster
- The standard American dictionary, and the best source of etymologies and usage notes.
- Oxford Learner's Dictionaries
- Every word with audio in British and American accents, plus collocations and example sentences. The best for learners.
- Phrasal Verb of the Day
- The complete dictionary of English phrasal verbs, freely available, with examples.
- Practice (learning method)
- Deliberate practice: what makes practice produce improvement and what does not.
- Spaced repetition
- The learning technique with the strongest evidence behind it, and the maths explaining why it works.
- Testing effect (retrieval practice)
- That recalling beats rereading. One of the most replicated findings in learning science.
- The Free Dictionary
- Several dictionaries in one, with a thesaurus and idioms alongside.
- Vocabulary learning
- The research literature on how words are actually acquired, and why reading beats word lists.
- Vocabulary.com
- Spaced-repetition vocabulary building, with a strong dictionary behind it.
- Wiktionary
- Open, multi-language, and unusually honest about regional variation and rare senses.
- Word frequency
- How frequency data is gathered and what it implies for which words to learn first.
- Word list
- Frequency lists, vocabulary size research, and what the '20,000 words' claim actually means.
- YouGlish
- Search for any word and hear it said in thousands of real videos. The fastest way to fix pronunciation of a new word.
- Zipf's law
- Why the second most common word appears about half as often as the first. The curve behind any frequency list.
English Writing & Composition
- Ambiguity
- Lexical, syntactic, scope and referential ambiguity. Understanding it makes writing clearer.
- American Rhetoric
- Annotated speeches and essays on delivery and persuasion. Free, and excellent for rhetorical analysis.
- Anaphora (linguistics)
- How pronouns and reference tie a sentence together, and the ambiguity that results when you are careless.
- Conceptual metaphor
- The Lakoff and Johnson work. Explains why argument is war, and why that is hard to undo.
- Connotation
- The emotional colouring a word carries. The thing that separates native-level writing from correct writing.
- Cooperative principle
- Grice's four maxims, and how to recover an intended meaning from a literally false utterance.
- Deixis
- 'This', 'there', 'then', 'I' — words whose meaning depends on context. A real hazard in formal writing.
- Denotation
- Literal meaning, as a separate thing from connotation. Useful for choosing precise words.
- George Mason University Writing Center
- Plain, practical guides on thesis statements, paragraph structure, editing and citation.
- Grammarly blog
- Well-researched articles on grammar and style. Some are marketing, many are genuinely good.
- LanguageTool
- Open-source grammar and style checking with good explanations. Works in a browser and as a LibreOffice add-on.
- Lexical analysis
- Tokenization and the pipeline underneath search, spell-checking and any NLP over text.
- Politeness theory
- Why indirect requests exist, and what native speakers expect under the surface. Directly useful in English.
- Pragmatics
- Meaning that lives outside the words. The gap between English as written and English as used.
- Register (sociolinguistics)
- How language changes by context. The single biggest factor in whether your English sounds wrong.
- Semantic ambiguity
- The kinds of ambiguity, and how to write sentences that do not generate them.
- Semantics
- Meaning in language, from word sense to sentence meaning to speech act. The core theory.
- Speech act
- Saying, asserting, promising, warning. Separating what you said from what you did by saying it.
- The EveryDay Writer's Guide
- Free chapters from Bedford's standard composition textbook, on drafting, revising and peer review.
Linux, Unix & Omarchy
Framework docs
- Actix Web documentation (free)
- The free official Actix Web docs. Comprehensive.
- Angular documentation (free)
- The free official Angular docs. Thorough, with good examples.
- Apache Spark docs (free)
- The free official Spark documentation. Big data, well documented.
- Astro documentation (free)
- The free official Astro docs. Very well organised.
- Axum documentation (free)
- The free Rust web framework docs. Well written, with real examples.
- Babylon.js documentation (free)
- The free official Babylon.js docs. Full engine for the web.
- bevy engine book (free)
- The free official Bevy book for the Rust game engine. Very good.
- Capacitor documentation (free)
- The free official Capacitor docs. Excellent for web-to-native.
- D3 documentation (free)
- The free D3.js docs. The standard for web data visualisation.
- Dagger documentation (free)
- The free Dagger docs. CI/CD pipelines as code, well explained.
- DHH — The Joy of Rails (free)
- DHH on why Rails is still the best way to build web apps. Persuasive.
- Django documentation (free)
- The free official Django docs. Exceptional depth and clarity.
- Django REST Framework (free)
- The free DRF docs. The standard for Python REST APIs.
- Drizzle ORM documentation (free)
- The free Drizzle docs. TypeScript-first SQL with great DX.
- Echo documentation (free)
- The free Echo framework docs. Good structure and examples.
- Elasticsearch guide (free)
- The free official Elasticsearch reference. Very thorough.
- Electron documentation (free)
- The free official Electron docs. Best reference for desktop apps.
- esbuild documentation (free)
- The free esbuild docs. Extremely fast bundler, tiny surface.
- Expo documentation (free)
- The free official Expo docs. Excellent for React Native.
- FastAPI documentation (free)
- The free official FastAPI docs. Excellent, with runnable examples.
- Fiber documentation (free)
- The free official Fiber docs. Very well organised.
- Flask documentation (free)
- The free official Flask docs. Clean and well written.
- Gin documentation (free)
- The free official Gin docs. Clear and practical for Go HTTP.
- gorm documentation (free)
- The free official GORM docs for Go. Clear and complete.
- Grafana documentation (free)
- The free official Grafana docs. Thorough and practical.
- htmx documentation (free)
- The free htmx docs. Tiny library, big idea. Very worth reading.
- Ionic documentation (free)
- The free official Ionic docs. Good cross-platform guides.
- Jest documentation (free)
- The free official Jest docs. The classic JS test runner.
- Kubernetes API reference (free)
- The free Kubernetes API reference. Precise and complete.
- Laravel documentation (free)
- The free official Laravel docs. Very thorough and well written.
- Next.js documentation (free)
- The free official Next.js docs. Comprehensive and current.
- OpenTelemetry docs (free)
- The free OpenTelemetry docs for traces, metrics and logs.
- OpenTelemetry protocol spec
- The free OpenTelemetry specification. Useful for interop work.
- Pandas documentation (free)
- The free Pandas docs. Good tutorials and complete reference.
- Playwright documentation (free)
- The free official Playwright docs. Excellent browser testing guide.
- Prisma documentation (free)
- The free official Prisma docs. Excellent ORM for typed data access.
- pytest documentation (free)
- The free official pytest docs. Excellent and thorough.
- PyTorch documentation (free)
- The free official PyTorch docs. Excellent tutorials and reference.
- Rails API documentation (free)
- The free official Rails API reference. Comprehensive.
- Rails documentation (free)
- The free official Rails guides. Still the best-written framework guides.
- React documentation (free)
- The free official React docs, rewritten to be genuinely good. Best React reference.
- React Native documentation (free)
- The free official React Native docs. Clear and thorough.
- Redis docs (free)
- The free official Redis documentation. Clear and well organised.
- Spring Boot reference (free)
- The free Spring Boot reference documentation. Very complete.
- Spring documentation (free)
- The free official Spring Boot and Spring docs. Comprehensive reference.
- sqlc — generate Go from SQL (free)
- Write SQL, get type-safe Go. Excellent docs in the repo.
- Storybook documentation (free)
- The free official Storybook docs. Component development in isolation.
- Svelte documentation (free)
- The free official Svelte and SvelteKit docs. Excellent and concise.
- Symfony documentation (free)
- The free official Symfony docs. Deep, rigorous, well structured.
- Tailwind CSS documentation (free)
- The free official Tailwind docs. Clear and practical.
- Tauri documentation (free)
- The free official Tauri docs. Good for Rust-based desktop apps.
- TensorFlow API docs (free)
- The free official TensorFlow API docs. Comprehensive reference.
- Terraform registry & docs (free)
- The free official Terraform docs and provider registry.
- Testing Library (free)
- Free docs for testing by user behaviour rather than implementation. Key idea.
- Three.js documentation (free)
- The free official Three.js docs. The standard for web 3D.
- Tokio documentation (free)
- The free Tokio docs. The best Rust async reference.
- Tonic documentation (free)
- The free Rust gRPC framework docs. Solid and clear.
- Unity Learn (free courses)
- Free Unity courses and tutorials. Very good for game dev.
- Unreal Engine documentation (free)
- The free official Unreal Engine documentation. Enormous and good.
- Vite documentation (free)
- The free official Vite docs. Excellent build tool for modern web.
- Vitest documentation (free)
- The free official Vitest docs. Modern, fast test runner for Vite.
- Vue documentation (free)
- The free official Vue 3 guide. Very well written and approachable.
- Web Components polyfills
- The free official Web Components polyfills. Web platform components.
- webpack guides (free)
- The free official webpack guides. The classic bundler reference.
Influential tech
- Accelerate (free excerpts)
- The research-backed DevOps book. Free excerpts on the site.
- Altair 8800 — the first personal computer
- Free Computer History Museum material on the Altair and the first PC era.
- Anders Hejlsberg — TypeScript
- The free TypeScript team blog on language design and releases.
- Ars Technica
- Free detailed tech journalism. Long-form and well researched.
- Basecamp — about
- Free essays on software, teams and work from DHH's company.
- Brian Kernighan — Bell Labs
- Brian Kernighan's page: books, courses, and UNIX history. Primary source.
- Changelog podcast
- Free podcast on software history, open source and developers. Excellent.
- Choose an open source license
- Free tool to pick a license. Clear, practical, important.
- Creative Commons licenses
- The free licenses for docs, data and code. Understand them properly.
- Darknet Diaries (free)
- Free podcast on real hacking and security stories. Compelling.
- DHH — Away from the office (announcement)
- DHH on remote work and trust. Influential writing.
- Doug McIlroy — Unix philosophy
- Doug McIlroy's page, with the original Unix papers and the pipe philosophy.
- Free Software Foundation
- The free software movement's foundation. Licenses and philosophy.
- GitLab Handbook (public)
- The best public engineering handbook. Free and very thorough.
- Guido's Python Design Guide
- The free official Python design rationale. Excellent on language design.
- IEEE Spectrum
- Free engineering journalism. Outstanding long-form and coverage.
- Internet Archive — classic computing texts
- Free scans of the classic computing books: K&R, Kernighan, Ritchie and more.
- James Gosling — The Java Language Spec
- The free official Java Language Specification. Primary source.
- Linus Torvalds — kernel mailing list
- Free archive of the Linux kernel mailing list. Historic and technical.
- Signals and Threads podcast
- Free podcast on the people behind Python and open source.
- Site Reliability Engineering resources
- Free SRE talks, case studies and the full book set. Very good.
- SPDX license list (free)
- The free authoritative list of open source licenses. Machine readable.
- Syntax.fm (free)
- Free web development podcast. Well produced and current.
- The Changelog — Ship It
- Free podcast on DevOps and deployment practice. Very practical.
- The GNU Manifesto (free)
- The free 1985 manifesto that started the free software movement. Read it.
- The GNU project
- The free GNU project portal. Stallman's philosophy in his own words.
- The Hacker's Manifesto
- Free home of the original 1984 manifesto. A foundational document. Read it.
- The Medium — DHH on Omakub
- DHH on the Ubuntu setup that preceded Omarchy. Good philosophy.
- The Mother of All Demos (free)
- Engelbart's 1968 demo. The video that shows what computing became.
- The Phoenix Project (free excerpts)
- The DevOps novel. Free excerpts and the site. Influential.
- The Pragmatic Engineer — podcast
- Free podcast on engineering management and industry analysis.
- The Register
- Free tech news with sharp, sceptical analysis. Very good reading.
- The Zen of Rails (DHH)
- DHH on why Rails' opinionated defaults win. Influential.
Language docs
- AsyncAPI specification (free)
- Free AsyncAPI docs for event-driven API contracts.
- Blender manual (free)
- The free complete Blender manual. Excellent reference for 3D.
- C# guide (Microsoft Learn)
- Free official C# guides from Microsoft. Modern and thorough.
- C2PA content credentials spec
- The free content provenance specification. Very relevant now.
- Clojure reference (free)
- The free official Clojure docs, guide and reference.
- CloudEvents specification (free)
- Free CloudEvents spec for portable event formats.
- Conventional Commits (free)
- The free commit message convention spec. Very useful in teams.
- cppreference — C reference
- Free, precise C language reference. Excellent for the standard library.
- Diátaxis documentation framework (free)
- The free framework for technical docs: tutorials, how-to, reference, explanation.
- ECMA-262 (ECMAScript spec)
- The free, living JavaScript standard, multipage version.
- ECMAScript specification (living)
- The free, living JavaScript standard. The ultimate authority.
- Elixir — Introduction (HexDocs)
- The free HexDocs introduction to Elixir. Best doc set in the BEAM world.
- Elixir documentation (free)
- The free official Elixir docs. Excellent, concise, well translated.
- Elixir official site
- The free official Elixir site: docs, guides and downloads.
- Elm guide (free)
- The free official Elm guide. The clearest introduction to FP web dev.
- Figma / design tokens spec
- The free W3C Design Tokens format spec. Increasingly important.
- GCC documentation (free)
- The free official GCC manual, including all the language options.
- GitHub Docs (free)
- The free official GitHub documentation. Authoritative and clear.
- GitLab docs (free)
- The free official GitLab documentation. Very thorough.
- GLSL / OpenGL reference
- The free Khronos OpenGL registry and specifications. Authoritative.
- GNU Emacs Lisp manual (free)
- The free complete Emacs Lisp manual. Essential for Emacs config.
- Go documentation (free)
- The official free Go docs, spec and effective Go. Essential reading.
- Godot documentation (free)
- The free official Godot engine docs and manual. Outstanding quality.
- GraphQL specification (free)
- The free official GraphQL specification. Clear and readable.
- Haskell documentation (free)
- Free links to the official Haskell docs, tutorials and libraries.
- IANA registries
- Free authoritative registries for ports, protocols, media types and more.
- Java documentation (free)
- The free official Java documentation, including the tutorials.
- JEPs — Java enhancement proposals
- Free index of all Java language and API proposals. See where Java goes.
- JSON Schema (free)
- The free JSON Schema specification. The standard for JSON validation.
- Julia documentation (free)
- The free official Julia docs. Excellent for a modern scientific language.
- JWT / JOSE RFCs
- The free primary source for JSON Web Tokens. Read the actual RFC.
- Keep a Changelog (free)
- The free changelog format spec. Adopt it for your projects.
- Kotlin standard library API (free)
- Free API docs for the Kotlin standard library.
- LLVM Language Reference
- The free official LLVM IR reference. Deep but readable.
- Lua reference manual (free)
- The free official Lua reference. Short, clean and complete.
- MDN — CSS reference
- The best CSS reference. Every property, value and browser note.
- MDN — JavaScript reference
- The best JavaScript documentation on the web. Authoritative and complete.
- MySQL reference manual (free)
- The free official MySQL manual. Comprehensive.
- Neovim Lua docs (free)
- The free official guide to configuring Neovim in Lua. Excellent.
- Nim manual (free)
- The free official Nim manual. Elegant systems language.
- Node.js documentation (free)
- The official free Node.js API docs. Comprehensive and clear.
- OCaml manual (free)
- The free official OCaml manual. For the serious functional programmer.
- OpenAPI Specification (free)
- The free OpenAPI specification. The API contract standard.
- OWASP API Security Top 10 (free)
- The free OWASP API Security Top 10. Essential for backend work.
- PHP documentation (free)
- The free official PHP manual. Comprehensive and well organised.
- PostgreSQL wire protocol
- The free Postgres frontend/backend protocol. Great systems reading.
- Python documentation (free)
- The official free Python docs, including the excellent tutorial.
- Python language reference
- The free official Python language reference. The precise details.
- Python tutorial (official)
- The free official Python tutorial. Clear and complete. Start here.
- R project (free)
- Free official R documentation, manuals and downloads.
- Redis protocol (RESP)
- The free official RESP protocol spec. Very short and clear.
- Ruby core API docs
- Free, fast, readable API docs for Ruby core and stdlib.
- Ruby documentation (free)
- Free official Ruby documentation. Well maintained and clear.
- Rust std docs (docs.rs)
- Docs for every crate on crates.io. The reference you will use daily.
- Semantic Versioning (free)
- The free SemVer specification. Two pages, should read it.
- SQLite file format (free)
- The free official SQLite file format spec. Fascinating systems reading.
- Unicode Standard (free)
- The free Unicode standard. The authority on characters and encoding.
- WebAssembly core specification (free)
- The free WebAssembly core spec. Surprisingly approachable.
Linux & Unix
- Alpine Linux
- Tiny secure Linux. Free docs and musl-based ecosystem. Good for containers.
- ALSA project documentation
- Free Linux sound architecture documentation. Needed for audio work.
- Arch Linux — general recommendations
- The core list of what to install and how to configure a good Arch system.
- Arch Linux — installation guide
- The most respected Linux install guide. Teaches you a lot by reading it.
- Arch Linux — list of applications
- A great curated list of the best app in every category on Linux.
- Arch Linux — list of applications: CLI
- Free curated list of the best command line tools by category.
- Arch Linux homepage
- The distribution Omarchy is built on. Simple, current, principled.
- Arch Linux man pages
- Free curated man pages for Linux. Clean, consistent and reliable.
- Arch Wiki
- The best Linux documentation on the web, by the community. Outstanding.
- atuin — shell history
- Free searchable, syncable shell history. Superb productivity upgrade.
- Awesome Linux Software
- A curated list of excellent Linux resources, apps and tools. Free.
- Babeltrace documentation
- Free open-source trace analysis tooling. Well documented.
- BashFAQ (ShellCheck wiki)
- The best bash FAQ on the internet. Read it and stop making the same mistakes.
- Bats-core (bash testing)
- Free open-source bash testing framework. Test your shell scripts properly.
- Beej's Guide to Network Programming
- Free sockets programming guide. Still the clearest introduction.
- Beej's Guide to Unix IPC
- A free, famously clear guide to Unix interprocess communication. Excellent.
- bpftrace
- Free open-source Linux tracing tool. eBPF without writing C.
- bpftrace docs
- The free bpftrace reference guide. Best way into eBPF scripting.
- Brendan Gregg — books
- Free companion sites for Systems Performance and BPF Performance Tools.
- btop — system monitor
- Free open-source resource monitor. Far better than top and htop.
- BusyBox
- A tiny multi-call Unix binary. Read its source to see minimal tool design.
- CMake documentation
- The free official CMake reference. Free and open source build system.
- Coreutils source
- Free source of the fundamental Unix tools. Read them to learn C.
- cppreference.com
- The best C++ reference on the web. Comprehensive and precise.
- D-Bus specification
- The free message bus spec. Underpins modern Linux IPC.
- Debian documentation
- Free official Debian docs, including the Administrator's Handbook.
- direnv — directory environments
- Free tool to load environment variables per directory. Very handy.
- DRM subsystem kernel docs
- The free kernel GPU userspace API documentation. Deep graphics detail.
- explained.dev
- Free short deep technical articles on programming topics. Very good quality.
- Free eBooks — Green Tea Press
- Free books on git, sed, Python and more. Excellent and short.
- FreeBSD handbook
- A free, outstanding Unix operating system handbook. The best OS text online.
- freedesktop.org specifications
- Free desktop standards: OpenGL, D-Bus, portals, screensaver. Authoritative.
- Gentoo Wiki
- Excellent in-depth documentation. The Portage system docs are superb.
- git-scm.com documentation
- The official free Git reference documentation for every command.
- GitHub — shellcheck
- Free open-source bash linter. Add it to CI immediately.
- glibc manual
- The free C standard library reference. Essential for systems programming.
- GNU Autoconf manual
- The free Autoconf manual. Deep but essential for C projects.
- GNU Autoconf manual (free)
- The free Autoconf manual. Essential for C projects.
- GNU C Library — C standard
- The GNU C Library home. Free manual and source.
- GNU Coreutils manual
- The free manual for the fundamental Unix utilities. Essential reference.
- GNU Debugger (GDB) manual
- The free official GDB documentation. The debugger's real power.
- GNU Emacs manual
- The complete free Emacs manual. Unmatched reference for an extensible editor.
- GNU Guix manual (free)
- A free, thorough manual on a complete, reproducible GNU system. Superb.
- GNU Manuals
- Free official manuals for coreutils, bash, make, gcc and more.
- GNU parallel (free)
- Free parallel shell job runner. Very capable, learn it.
- htop (process viewer)
- Free interactive process viewer. A better top. Ubiquitous and essential.
- jq — JSON processor
- Free command-line JSON processor. The most useful tool in the shell.
- Kernel.org
- The canonical source for kernel releases, patch announcements and docs.
- Kernel.org — eBPF verifier
- The free kernel BPF documentation. Deep and authoritative.
- KernelNewbies
- Free friendly community for people learning kernel development. Great starting point.
- Linux audio: JACK and PipeWire
- Free site for PipeWire, the modern Linux audio server. Read the docs.
- Linux Documentation Project
- HOWTOs and guides for every aspect of Linux administration. Huge archive.
- Linux Foundation training (free)
- Free Linux and cloud training courses and certifications. Genuinely free.
- Linux in a Nutshell (O'Reilly, free)
- A free concise reference for Linux commands and administration.
- Linux kernel coding style
- The official kernel coding style guide. Short, strict and instructive.
- Linux kernel source (git)
- The kernel source. Read subsystems to understand how Linux really works.
- Linux System Administrator's Guide
- A free classic book on Linux system administration. Still relevant.
- Meson build system
- A fast, modern build system. Clean documentation and a good model.
- Modern Perl and the Modern Perl Weblog
- Free books on Perl and related languages. A huge amount of material.
- musl libc
- A free, small, correct C library. Read the docs on its deliberate differences.
- ncdu — disk usage
- Free ncurses disk usage analyser. The best way to find what ate your space.
- NetBSD documentation
- Free BSD documentation. Clean, thorough and well organised.
- Ninja build tool
- Free tiny build tool used by Chromium and others. Manual is short and clear.
- nixOS manual (free)
- The free Nix manual. Excellent and complete for a modern Linux system.
- OpenBSD FAQ and man pages
- Free OpenBSD FAQ and the cleanest man pages of any Unix.
- OpenSSH portable
- Free open source SSH. The manual is the best reference for ssh_config.
- PipeWire documentation
- The free PipeWire documentation. Essential for modern Linux audio.
- pkg-config / Meson
- Free freedesktop.org guide to building and installing shared libraries correctly.
- POSIX standard (The Open Group)
- The free POSIX specification. What makes a program genuinely Unix.
- PulseAudio documentation
- Free PulseAudio documentation, still relevant for older systems.
- quilt / git — patch workflows
- The free kernel doc on submitting patches. Great for learning code review.
- r/linux
- Active Linux community for questions, news and troubleshooting.
- r/UnixPorn (dotfiles)
- Free community showcasing rices, dotfiles and desktop setups. Great inspiration.
- Red Hat documentation
- Free, deep enterprise Linux documentation from Red Hat. Excellent.
- ripgrep guide
- The free official ripgrep guide. Best patterns guide for searching code.
- ShellCheck
- Free static analysis for bash scripts. Catches bugs before they bite.
- shfmt (shell formatter)
- Free open-source shell formatter. Run it, commit the result.
- SSH manual (OpenSSH)
- The free official OpenSSH manual. Config, options and the protocol.
- strace and ltrace
- Free syscall tracer. The single most useful Linux debugging tool. Learn it.
- Sysdig open source tools
- The bcc and bpftrace home. Free Linux observability tools.
- systemd-analyze docs
- Free systemd-analyze reference for boot and performance analysis.
- systemd.io
- The free systemd documentation, including the excellent journal docs.
- systemd.io — debugging systemd
- Free official guide to debugging systemd services. Extremely useful.
- The Linux Foundation
- Free resources, training and documentation from the Linux Foundation.
- The Linux Kernel documentation
- The authoritative kernel docs. Huge, deep and free. The core reference.
- The Linux Programming Interface (free)
- Kerrisk's definitive systems programming book. Free code and the man pages.
- The Open Group — Unix resources
- Home of POSIX and the Open Group. Free standards and resources.
- Ubuntu documentation
- Official Ubuntu desktop and server docs, now nicely restructured.
- Void Linux handbook
- Free docs for an independent, fast, rolling-release Linux. Clean and sharp.
- Vulkan and Mesa drivers
- Free Mesa 3D documentation. Understand your graphics stack.
- Wayland protocol and compositors
- Free Wayland protocol specifications and documentation.
- WireGuard (free)
- A free, tiny, fast VPN. The protocol paper is short and excellent.
- WirePlumber documentation
- Free session manager docs for PipeWire. Very thorough.
- X.Org documentation
- Free X Window System documentation, protocols and specifications.
- zlib / zstd documentation
- Free zstd documentation. Great practical compression reference.
Omarchy
- AI agents
- How Omarchy sets up coding agents and gives them system skills.
- Common tweaks
- The most common customizations, written up. Very high value.
- DHH — Omarchy 2.0
- DHH's tour of the 2.0 release. Shows the whole system in screenshots.
- DHH — Omarchy is out
- DHH's original announcement. Read it to understand the intent and philosophy.
- DHH's blog (world.hey.com/dhh)
- David Heinemeier Hansson's writing on Rails, Omarchy, AI and work.
- Dotfiles
- How dotfiles work in Omarchy, and how to keep them across machines.
- Getting Started
- Official install guide: ISO, BIOS settings, encryption, dual boot. Start here.
- Hotkeys
- Complete keyboard reference. Super + Space menu, workspaces, clipboard, screenshots.
- Hyprland — official site
- The tiling Wayland compositor Omarchy is built on. Full docs and wiki.
- Hyprland wiki
- The complete Hyprland documentation: config, animations, plugins, rules.
- Learn.omacom.io — manual mirror
- Mirrored manual with screenshots. Very useful for visual reference.
- Making your own theme
- Build a custom theme from scratch. Good first customization project.
- Navigation & Workspaces
- How tiling, workspaces and the top bar work. Core mental model.
- Omakub (Ubuntu sibling)
- DHH's opinionated Ubuntu setup — the sister project to Omarchy.
- Omarchy — development tools
- How languages and toolchains are installed. Mise handles versions.
- Omarchy — official site
- Beautiful, fun & agentic Linux by DHH. Arch + Hyprland + Quickshell, fully configured.
- Omarchy 3 manual (legacy)
- The manual for the previous major version, kept for older installs.
- Omarchy CLI
- The `omarchy` command: scriptable control of the whole system. Agents love it.
- Omarchy on GitHub (basecamp)
- The original repository. Same project, original org. MIT licensed.
- Omarchy on GitHub (omacom/omarchy)
- The source. The manual lives in `manual/` and is the source of truth. MIT licensed.
- Prompt & shell
- The default shell, prompt and the files that drive them.
- Quickshell
- The desktop shell toolkit Omarchy's bar and menus are built with. QML-based.
- Security
- Encryption, Secure Boot, and the security model. Well explained.
- Shell plugins
- Extend the shell with extra tooling. The recommended integration point.
- System snapshots
- Btrfs snapshots and how to roll your system back. Very important to understand.
- The Omarchy Manual
- The authoritative manual. Every feature, hotkey, config and workflow. Read this.
- Themes
- How Omarchy theming works and how to switch between the bundled themes.
- Toggles, idle & screensaver
- Automatic behaviour on idle, and the screensaver. Practical details.
- Troubleshooting
- Official fixes for common problems. First place to look when something breaks.
- Unattended installs
- Automate the Omarchy install. Useful for testing and multiple machines.
- Unified clipboard & history
- How clipboard sharing and history work between machines. Very useful.
- Updates
- How Omarchy updates work, including AUR and the mirror strategy.
Technical writing
- A11Y project checklist
- The free A11Y Project checklist. Use it before shipping anything.
- Accessibility for developers
- The free ARIA Authoring Practices Guide. How to build accessible widgets.
- C4 model diagrams (free)
- Free guidance on drawing useful architecture diagrams.
- Communicating technical topics — W3C
- The free WCAG 2.2 understanding documents. Accessibility for authors.
- Content Design — GOV.UK style guide (free)
- The free GOV.UK content design guide. Exemplary official writing.
- Divio documentation system
- The free documentation system that Diátaxis is based on. Clear intro.
- Docs as code (free)
- Free guide to managing documentation with version control.
- Docusaurus documentation (free)
- Free docs site generator. Excellent for technical documentation.
- Excalidraw hand-drawn style (free)
- Free hand-drawn style diagrams. Much easier to make and to read.
- GitHub Pages (free hosting)
- Free static site hosting for documentation. Zero cost.
- Google Developer Documentation Style Guide (free)
- The free Google style guide. The best practical writing reference.
- markdownlint
- Free markdown linter. Keeps your READMEs consistent.
- mdBook — Rust book tool (free)
- Free book/documentation tool written in Rust. Very fast.
- Microsoft Writing Style Guide (free)
- The free Microsoft style guide. Very thorough and practical.
- MkDocs Material (free)
- Free, beautiful documentation sites from Markdown. Outstanding theme.
- Nielsen Norman Group articles (free)
- Free research-based UX writing and usability articles. Excellent.
- Plain Language movement (free)
- The free US government plain language guidelines. Practical writing rules.
- Sphinx documentation (free)
- The free documentation generator. Mature and powerful.
- Vale — prose linter
- Free open-source prose linter. Enforce your style automatically.
- Web Content Accessibility Guidelines
- The free WCAG standard. Essential for anyone shipping a UI.
- Write the Docs (free)
- Free guides on documentation best practices from the community.
Papers, Books & Blogs
Free textbooks
- Alberts — Molecular Biology of the Cell (NCBI)
- The definitive cell biology textbook, free in full on the NCBI Bookshelf.
- BCcampus Open Textbooks
- Excellent free open textbooks: anatomy, chemistry, physics, nutrition, health.
- Becker, Becker & Schwarz — String Theory and M-Theory
- Free comprehensive string theory textbook PDF from Hawaii.
- BRS Pathology review (free outlines)
- Free pathology outlines for every organ, essentially a textbook online.
- David Tong — Statistical Physics notes
- Free complete statistical physics course notes from Cambridge.
- Digital Histology (SIU)
- Free interactive histology course with high-resolution micrographs.
- Goodman & Gilman — The Pharmacological Basis of Therapeutics
- The authoritative pharmacology text, free to read on NCBI.
- Guyton and Hall — Textbook of Medical Physiology (NCBI)
- The classic physiology reference, free to read on the NCBI Bookshelf.
- Junqueira — Basic Histology (NCBI)
- Standard histology text, free on NCBI. Pairs with the free histology sites.
- Kandel — Principles of Neural Science (NCBI)
- The definitive neuroscience textbook, free in full. Outstanding resource.
- Khan Academy — full subject list
- Free K-12 to university material in maths, science, medicine and computing.
- LibreTexts
- Thousands of free, peer-reviewed, remixable textbooks across every science.
- LibreTexts — Biology
- Free biology textbooks, from microbiology to genetics to ecology.
- LibreTexts — Chemistry
- The most complete free chemistry textbook collection anywhere.
- LibreTexts — Human Biology
- Free human biology, nutrition and physiology material.
- LibreTexts — Medicine
- Free medical subject pages: anatomy, physiology, pathology, pharmacology.
- LibreTexts — Physics
- Free physics texts: mechanics, EM, thermodynamics, quantum.
- MIT OCW — 5.111 Chemical Science index
- The free MIT chemistry sequence, with videos and full problem sets.
- MIT OCW — String Theory
- Free MIT string theory courses. The best place to start with strings.
- Open Oregon — open textbooks
- Free peer-reviewed textbooks in anatomy, physiology, chemistry and physics.
- OpenStax
- Free, peer-reviewed, CC-licensed textbooks for majors. The best starting point.
- OpenStax — Anatomy & Physiology 2e
- Complete free A&P textbook. Covers every system with clear diagrams.
- OpenStax — Anatomy & Physiology index
- Browse every free science textbook OpenStax publishes.
- OpenStax — Astronomy
- Free astronomy from naked-eye observation to cosmology.
- OpenStax — Biology 2e
- Free intro biology: cells, genetics, evolution, ecology.
- OpenStax — Chemistry 2e
- Free intro chemistry with worked problems and solutions.
- OpenStax — College Physics 2e
- Free algebra-based physics with real-world applications.
- OpenStax — Introductory Statistics
- Free statistics textbook with examples drawn from medicine and biology.
- OpenStax — Microbiology
- Free microbiology with clinical relevance throughout.
- OpenStax — Statistics for health research
- Free statistics and biostatistics textbooks for reading medical papers.
- OpenStax — University Physics Vol 1
- Free calculus-based physics: mechanics, waves, thermodynamics.
- OpenStax — University Physics Vol 2
- Free electricity, magnetism, waves, optics and thermodynamics.
- Preskill — Quantum Information and Computation (Caltech)
- Free complete course notes on quantum information. Rigorous and beautifully clear.
- Pressbooks (BCcampus collection)
- Hundreds of free open textbooks, browsable by subject.
- Project Gutenberg — Books in Medicine
- Darwin, Maxwell, Faraday and more, free and complete.
- Schwartz — QFT and the Standard Model (free PDF)
- Free textbook covering QFT and the Standard Model. Very good and approachable.
- Shotgun Histology
- Free concise histology reference with labelled slides and videos.
- Srednicki — Quantum Field Theory (free online)
- A complete QFT textbook, free to read online. Rigorous and self-contained.
- The Feynman Lectures — Caltech
- Full text index of all three volumes plus the 1964 challenge course.
- The Feynman Lectures on Physics
- Free, digitized, complete. The best physics textbook ever written.
- University of Michigan Histology
- Free slide-based histology course from a top department.
- WebPath — University of Utah Pathology
- The classic free pathology image atlas. Tens of thousands of annotated images.
- Wheater's Histology Guide
- Free, image-rich histology course with virtual microscope slides. Superb.
- Wikibooks
- Free, community-written textbooks including Physics and Chemistry 1.
- Wikipedia — portal: science
- The free encyclopedia is genuinely the best quick reference. Start from these portals.
Papers & preprints
- AlphaXiv
- Free AI summaries of arXiv papers. Excellent way to triage new papers fast.
- arXiv
- The open preprint server that changed science. Free, immediate, 2M+ papers.
- arXiv — Astrophysics (astro-ph)
- Cosmology, galaxies, stars, instruments, exoplanets.
- arXiv — Computer Science (recent)
- The CS firehose: AI, systems, theory, graphics, crypto. Filter by category or author.
- arXiv — Condensed Matter
- Materials physics, superconductivity, quantum matter. Free preprints.
- arXiv — Cosmology (astro-ph.CO)
- CMB, inflation, dark matter, large-scale structure.
- arXiv — General Relativity (gr-qc)
- Gravitation and relativity preprints. Free and current.
- arXiv — hep-ph
- High-energy physics theory: QCD, electroweak, beyond Standard Model.
- arXiv — High Energy Physics (hep-ex)
- High-energy phenomenology: the particle physics phenomenology archive.
- arXiv — Math & Statistics
- Statistics and machine learning theory, free preprints.
- arXiv — Mathematics
- All of mathematics as preprints.
- arXiv — Nuclear Experiment (nucl-ex)
- Nuclear experimental physics preprints. Free.
- arXiv — Nuclear Theory (nucl-th)
- Nuclear structure and heavy-ion theory.
- arXiv — Physics archive
- All of physics: astro-ph, cond-mat, gr-qc, hep-*, nucl-*, physics.*
- arXiv — Quantitative Biology (q-bio)
- Free quantitative biology: bioinformatics, biophysics, systems biology.
- arXiv — Quantum Physics (quant-ph)
- Quantum mechanics, quantum information, quantum computing.
- arXiv — Soft Condensed Matter (physics)
- Soft matter and complex systems. Free preprints.
- BASE — Bielefeld Academic Search
- Free search across hundreds of institutional repositories.
- bioRxiv
- Biology preprints, before publication. Free full text, no paywall ever.
- BMC — journals
- Hundreds of BMC open access journals, all free to read.
- CERN Document Server
- Half a million high-energy physics papers, free full text.
- chemRxiv
- The preprint server for chemistry, run by the ACS.
- CiteSeerX
- Free citation graph and search for computer science literature.
- Connected Papers
- Build a graph of related papers from one seed. See the shape of a field.
- Consensus
- Free search that answers questions across peer-reviewed papers. Free tier.
- CORE
- The world's largest aggregator of open access research papers.
- Crossref search
- Search the DOI registry directly. Find papers and resolve DOIs.
- Data availability statements
- Crossref metadata and funder data policies. Useful for finding open versions.
- DBLP — CS bibliography
- The authoritative free bibliography of computer science. Open data.
- DOAJ — Directory of Open Access Journals
- Filter to only fully free, open access journals. Honest and vetted.
- Elicit
- Free AI literature review assistant that extracts findings across papers.
- eLife
- Open access life sciences journal with open peer review. Free to read.
- Emergentmind
- Free daily digest of research papers with community discussion. Very good.
- Europe PMC
- Better search than PubMed, free full text, includes preprints and patents.
- Frontiers — open access journals
- Fully open access journals across science, health and engineering. Free.
- Google Scholar
- The best search coverage of all time. Free; use it to find free PDFs.
- HEPData
- Free submission data from every major particle physics experiment. Primary data.
- ICPSR — social science data
- Free archive of social science data and documentation. Also health and economics.
- Inspec
- IET's freely readable engineering and physics journal.
- INSPIRE HEP literature search
- Literature search built for particle physics. The standard tool.
- Journal of Chemical Physics (AIP)
- AIP's flagship chemical physics journal. Free abstracts, some open access.
- Litmaps
- Free tool to map the literature around a topic and follow authors.
- Mathematics Stack Exchange
- Rigorous Q&A for mathematical physics and pure maths.
- MDPI — open access journals
- 600+ fully open access journals: Nutrients, Materials, Pharmacy, IJMS.
- medRxiv
- Health sciences preprints: epidemiology, clinical trials, public health.
- Nature Physics — latest
- Top physics journal. Free to read selected articles, abstracts always free.
- Nature Reviews — free content
- Authoritative reviews; some content free, and abstracts are always readable.
- NCBI Bookshelf
- Free authoritative medical books online, including StatPearls.
- NCBI E-utilities & API
- The API docs behind PubMed and PMC. Programmatic access to all literature.
- OpenAIRE Explore
- Free portal to European open access papers across all disciplines.
- OpenAlex
- Open catalogue of 200M+ scholarly works with APIs. Fully open data.
- ORCID
- Free persistent researcher identifier. Connects all your output.
- OSTI — US govt science reports
- Free full text of DOE and US government technical reports. Underexplored.
- Physical Review — open access
- APS journals, with an increasing fully open access portfolio. Free register.
- Physical Review Letters (APS)
- APS flagship. Free to read many articles; all metadata open.
- PLOS — journals
- PLOS ONE, PLOS Medicine, PLOS Biology and more. Fully open access, no fees to read.
- PLOS Biology
- Fully open access flagship biology journal. Free to read in full.
- Preprints.org
- Multidisciplinary preprint server across sciences, maths and humanities.
- PubMed
- The NIH index of biomedical literature. Free abstracts, links to full text.
- PubMed Central (PMC)
- The NIH free full-text archive. Millions of papers, zero paywall.
- Research Rabbit
- Follow authors and collections; get alerted to new papers. Free.
- ScienceOpen (free abstracts)
- Free access to a large collection of open access articles.
- Scientific Reports
- Multidisciplinary open access journal from Nature. Everything free to read.
- SciSpace
- Free AI reader for papers with explanation and chat. Good for dense PDFs.
- Semantic Scholar
- AI-assisted paper search with citation context. Free account, good free tier.
- Semantic Scholar API
- Free API for paper search, citations and recommendations. No key needed to start.
- SSRN — free papers
- Social science preprints; some full texts free.
- The Journal of Chemical Physics — Editors' Choice
- Free selection of notable papers across chemical physics.
- The Lens — scholarly works
- Free scholarly database with patent and citation links. Good for literature review.
- Undermind
- Free AI search tuned for technical and scientific queries.
- Unpaywall
- Find the legal free PDF of any paywalled paper, given a DOI.
- World Bank Open Data
- Free development, health and economics indicators for every country.
- Zenodo — CERN repository
- Free DOI for any research output, hosted by CERN. 60M+ records.
Topic blogs
- ALMA Observatory
- Free site for the Atacama Large Millimeter Array. Excellent science and images.
- Ask an Astronomer
- Free answers to astronomy questions from working professionals. Very good.
- CERN — Social Sciences
- Free CERN science pages: detectors, accelerators, computing. Very clear.
- Chemistry Stack Exchange
- Free Q&A for chemistry calculations, theory and technique. Very useful.
- Chronically Diverse
- Free blog on astrophysics, physics, and being a scientist. Outstanding writing.
- Clinical Gate
- Free full-text chapters from major Elsevier medical and physiotherapy textbooks.
- Darwin Online
- Free full text of Darwin's published and unpublished writing. Primary source.
- eBird — Cornell Lab
- Free global bird observation database. Genuinely useful citizen science.
- Encyclopedia of Life
- Free, free-to-use species pages drawing from all the major databases.
- Evidence Checked
- Free nutrition blog reviewing the evidence behind diet claims. Very careful.
- GBIF — Global Biodiversity Facility
- Free global biodiversity data infrastructure and API. Open data.
- Gemini Observatory
- Free science and imagery from the Gemini 8m telescopes.
- IAEA Nuclear Knowledge Portal
- Free official resources on nuclear science, safety and applications.
- iNaturalist
- Free biodiversity observations with AI-assisted species identification. Huge dataset.
- Khan Academy — Health & Medicine
- Free medicine courses: anatomy, pharmacology, infectious disease, neurology.
- Learning Radiology
- Free radiology education site with cases and quizzes. Very usable.
- MedBullets
- Free tier with strong topic-by-topic medical study guides.
- MedlinePlus — Nutrition
- Free plain-language nutrition information from the NIH.
- Molecule of the Month (Bristol)
- Free monthly deep dive into one molecule. Superb chemistry writing.
- NASA Space Place
- Free NASA site for young learners and educators. Great for teaching and intuition.
- NCCIH — complementary health evidence
- Free NIH evaluations of complementary and alternative medicine. Very useful.
- NIH Office of Dietary Supplements
- Free, authoritative fact sheets on every supplement and nutrient.
- Ninja Nerd
- Free, exhaustive medical teaching videos. Effectively a free medical course.
- Nuclear Regulatory Commission — basics
- Free official reference on radiation, dosimetry and regulation.
- Nutrition Advance
- Free, evidence-focused nutrition blog that reads the actual studies.
- Osmosis free learning
- Free video lessons on medicine and biology. Some content open without payment.
- Periodic Videos
- Free short videos on every element. The best chemistry channel there is.
- Pharyngula
- Free blog curating evolution, palaeontology and developmental biology posts.
- Precision Nutrition blog
- Free blog on personalising nutrition from your own data. Rigorous and free.
- Quantum Computing Report
- Free news and analysis on quantum hardware and software. Regular.
- Quantum Computing Stack Exchange
- Free Q&A on quantum algorithms, error correction and hardware.
- Radiology Key
- Free companion site to radiology textbooks, chapter by chapter.
- Serious Eats
- Free food science and technique explained rigorously. Now part of Serious Eats/Dotdash.
- Sloan Digital Sky Survey
- Free site and data release from one of the great public surveys.
- Small Things Considered (ASM)
- The American Society for Microbiology blog. Free, well-written, daily.
- Space.com
- Free space news and science. Accessible and well illustrated.
- TalkOrigins
- Free archive of the best creationism-vs-evolution arguments. Excellent reference.
- The Kenji Lopez-Alt blog
- Free, deeply researched food science writing. The modern food-lab reference.
- The Owl (OWL — open textbook library)
- Free directory of vetted open textbooks across every subject, including health.
- The Panda's Thumb
- Free, long-running evolution blog from a working evolutionary biologist.
- The Planetary Society
- Free space advocacy and science outreach from a well-known non-profit.
- The Quantum Journal
- Free student-led journal about quantum physics. Accessible papers.
- This Week in Virology
- Free weekly podcast and blog on virology. Long-running and excellent.
- Universe Today
- Free space and astronomy news site, very active and well sourced.
- World Nuclear Association
- Free, information-rich site on nuclear energy, technology and fuel cycle.
- XKCD — What If
- Free webcomic answering speculative physics questions. Genuinely educational.
Fun & News
Fun facts
- 3Blue1Brown (YouTube)
- The best visual math explanations ever made. Truly brilliant.
- Aeon Essays
- Long-form philosophy, science and society essays. Free and excellent.
- Chrome Music Lab
- Fun experiments with music, rhythm and the Web Audio API.
- Computer History Museum
- The definitive computing museum. Articles and exhibits are free online.
- Computerphile (YouTube)
- Short academic CS videos on compression, cryptography, AI. Superb.
- Explain XKCD
- Deep explanations of xkcd comics. Surprisingly good technical writing.
- Fireship (YouTube)
- Very fast, very dense tech explainers. Perfect for a quick overview.
- Information is Beautiful
- Award-winning data visualization and infographics. Great for intuition.
- Internet Archive
- Web archive, old software, films and books. An endless time machine.
- jz's blog (jwz.org)
- Java/XML/original sin, and a very funny, technically sharp writer.
- Kurzgesagt
- Beautiful, accurate explainers on science and tech. Great rabbit hole.
- Longreads (Longreads.com)
- The best long-form journalism on the web. Free to read.
- Low Level Learning (YouTube)
- Deep x86, assembly, OS and hardware internals. A treasure trove.
- Nautilus
- Science stories with a philosophical bent. Genuinely interesting.
- Numberphile (YouTube)
- Math and number facts with mathematicians. Endlessly entertaining.
- Old Computer Museum
- Photos and specs of vintage hardware. Great for nostalgia and context.
- Open Library
- A free library catalog with borrowable scanned books.
- Our World in Data
- The best data visualizations on human history and modern issues.
- Programming is Terrible
- Relatable satire about real-world software. Funny and true.
- Project Gutenberg
- Over 70,000 free ebooks. The public domain, unlimited.
- r/ProgrammingHorror
- Real code and stories that will keep you humble. Great fun reads.
- Radio Garden
- Explore live radio stations on an interactive globe. Delightfully calming.
- The Effective Engineer (Will Larson)
- Engineering effectiveness essays. Practical and thoughtful.
- The Marginalian
- Maria Popova on literature, art and meaning. Wonderfully written.
- The Old Net
- Access classic websites from the early web. Delightfully weird.
- The Prepared (technology policy)
- Deep reporting on technology, government and power. Excellent.
- The Public Domain Review
- Beautiful essays on art, literature and science from public-domain works.
- The Wayback Machine
- Snapshots of any public webpage over time. Great for research nostalgia.
- This Person Does Not Exist
- GAN-generated faces. A good demo of what modern models can do.
- Two Minute Papers (YouTube)
- Fast, readable summaries of the latest ML papers. Great habit.
- Wait But Why
- Illustrated long-form explanations of AI, Elon, and the future. Long, but gripping.
- Wait, another link?
- Essays on technology, incentives and society. Thought-provoking.
- xkcd
- Webcomic about nerds. The 'What If' series is great for CS intuition.
News & aggregators
- Awesome Go
- A huge, well-categorized list of Go libraries and tools.
- Awesome Rust
- A massive, categorized list of Rust crates and resources.
- Awesome Selfhosted
- Thousands of free, open-source self-hostable apps.
- DEV — Android tag
- Community Android articles and discussions.
- DEV — Flutter tag
- Community Flutter articles and discussions.
- DEV — Rust tag
- Community Rust articles and discussions.
- Dev.to (DEV Community)
- Huge developer blogging platform with real, practical posts.
- Feedbin trial
- Solid hosted RSS reader if you don't want to self-host.
- Hacker News front page
- news.ycombinator.com — the original. Use lobste.rs to filter the noise.
- Hacker News RSS
- RSS feeds for Hacker News (front page, best, newest).
- Hashnode
- Developer blogging with good community and free tier.
- Inoreader / FreshRSS
- Self-hostable RSS reader. Perfect for all these bookmarks.
- Lobsters — databases tag
- Database internals and data engineering links.
- Lobsters — Go tag
- Curated Go links and discussions.
- Lobsters — Linux tag
- Curated systems and kernel links with real discussion.
- Lobsters — programming tag
- General programming links worth your time.
- Lobsters — Rust tag
- Curated Rust links and discussions.
- Lobsters (Hacker News for hackers)
- Tag-based link sharing with a much better signal-to-noise ratio than HN.
- Public GitHub Trending
- See what's rising across languages. Good weekly habit.
- Techmeme
- Tech news aggregator with links to primary sources. Fast.
- TLDR newsletter
- Concise daily tech news digest. Subscribe free, read in five minutes.
Hacking & Pentesting
Go Hacking
- Amass — attack surface discovery
- OWASP's Go toolchain for mapping your own or an authorised attack surface. The most thorough free option.
- dalfox — XSS scanner
- A fast Go cross-site-scripting scanner with analysis, Bypass and reporting built in.
- ffuf — web fuzzer
- Fast, configurable content discovery written in Go. Recalibration and auto-calibration make it far less noisy than older fuzzers.
- gitleaks — secret scanning
- Finds hardcoded credentials in git history. Run it on your own repositories; the results are frequently alarming.
- Go 1.21 release notes
- A readable summary of what each recent Go release added, including fuzzing and the race detector improvements.
- Go fuzzing in the standard library
- Go has native fuzzing support, and this is the service that runs it continuously on thousands of projects.
- gobuster — directory and file brute force
- The long-standing Go brute-forcer for directories, files and S3 buckets.
- gosec — Go security analyser
- Static analysis for Go source, finding integer overflows, weak crypto and injection patterns.
- govulncheck
- The official Go vulnerability scanner. Reports only vulnerabilities your code can actually reach, which makes it unusually low-noise.
- httpx — HTTP probing
- Spray and probe thousands of hosts for live web services. Go, fast, and pipeline-friendly with the rest of ProjectDiscovery.
- katana — web crawler
- A concurrent crawler in Go tuned for finding endpoints and parameters in JavaScript-heavy sites.
- naabu — port scanner
- A fast SYN-scan port scanner written in Go that feeds straight into httpx.
- nuclei — template-driven scanner
- A fast scanner driven by community templates, written in Go. Extremely extensible.
- OpenSSF Scorecard
- Automated security posture scoring for any open-source project. Free and works on any public GitHub repo.
- OWASP Software Component Verification Standard
- Free guidance on verifying the components you depend on, which is where supply-chain risk actually lives.
- Scorecard web interface
- Paste a repository URL and get its security posture scored. Useful for vetting dependencies before you adopt them.
- Sliver — C2 framework in Go
- An open-source, Go-based command and control framework. Study the protocol and the implant to learn how C2 actually works.
- staticcheck and go-tools
- A deep static analysis suite for Go that catches far more than the compiler does. Also the basis of golangci-lint.
- subfinder — subdomain enumeration
- Fast, Go-based passive subdomain discovery. The starting point of nearly every recon workflow.
- trufflehog — secret detection
- Deeper secret scanning with verification, and it understands credential formats rather than just patterns.
Hacking & Pentesting
- AFL and libFuzzer — fuzzing
- Coverage-guided fuzzing. The most effective way to find bugs and crashes in parsers.
- bettercap — network reconnaissance and PoC
- Free, open-source tool for network monitoring, MITM and protocol experimentation on your own networks.
- crt.sh — certificate transparency search
- Free, complete search over certificate transparency logs. Excellent subdomain discovery.
- Cutter — Rizin GUI
- Graphical frontend for Rizin and radare2, comparable to commercial disassemblers.
- DEF CON — conference archive
- Every DEF CON talk, free and archived. Hours of deep technical security material.
- DEF CON conference
- The hacker conference. Free talks, archives and the Hacker Village for hands-on work.
- Exploit Database
- A free archive of real exploits and proof-of-concept code, with references.
- Firmware analysis with binwalk
- Extracts and analyses embedded firmware images. Open source and essential for device research.
- FIRST — CVSS and vulnerability scoring
- The official specification and calculator for the CVSS severity scoring system.
- GDB — the GNU debugger
- The standard native debugger. Learning GDB properly is one of the highest-leverage skills in systems work.
- Ghidra — reverse engineering
- The NSA's free, open-source decompiler and reverse engineering suite. Extremely capable.
- Ghidra source (GitHub)
- The full open-source codebase, with excellent documentation for extending it with new languages.
- Hack The Box
- Practical hacking labs ranging from easy to very hard. Free tier available.
- HackTricks — the pentesting notes
- An extremely detailed free knowledge base of offensive techniques, from recon to pivoting.
- IoT and embedded hacking resources
- Free collections of tools and firmware analysis material for embedded device research.
- John the Ripper and hashcat
- Free password auditing tools. Legitimate for testing your own credential strength and recovery options.
- JTAG and hardware hacking primer
- Public hardware research tools and notes for reading out and debugging devices via JTAG and SWD.
- Legal and ethical hacking guidance (GetFreeOnlineCourses)
- Free structured cybersecurity courses, several covering radio and network security defensively.
- Metasploit Framework
- Free, open-source penetration testing framework. The standard exploitation toolset.
- MITRE ATT&CK
- The free, complete knowledge base of adversary tactics and techniques. Free and open.
- MITRE ATT&CK for ICS and radio
- The same framework applied to industrial and control systems, including radio interfaces.
- NIST Cybersecurity Framework
- The free, widely adopted framework for organising defensive security work.
- OpenVAS / Greenbone
- Free, open-source vulnerability scanner. A legitimate self-assessment tool for your own systems.
- OverTheWire: Wargames
- Classic SSH and security wargames, entirely free, from absolute beginner upward.
- OWASP Web Security Testing Guide
- The free, open-source methodology for testing web applications. Comprehensive and free.
- PayloadsAllTheThings
- An exhaustive free reference of payloads, techniques and evasion methods by category.
- picoCTF
- Free, gamified security challenges created for high school students but genuinely good.
- Pulsedive — threat intelligence
- Free threat intelligence platform with a genuinely useful free tier.
- pwn.college
- Free, deep binary exploitation course with a real grading system. Excellent for systems hacking.
- QEMU — machine emulation
- Full system and user-mode emulation. Lets you inspect hardware behaviour from software.
- Responder — LLMNR/NBT-NS poisoning
- Explains and demonstrates Windows name resolution attacks. Study it to defend your network.
- rizin and radare2
- Free, open-source reverse engineering frameworks. radare2 is a superset of the classic disassembly workflow.
- SecLists — the wordlists collection
- The definitive free collection of wordlists for security testing. Enormous and well organised.
- SecurityTrails (passive DNS)
- Free tier passive DNS and historical DNS records, useful for understanding infrastructure.
- Shodan — internet-exposed devices
- Free search engine for internet-connected devices. Powerful for learning what is exposed.
- Software Defined Radio security research
- GNU Radio's own notes on radio protocol security and research methodology.
- The Hacker Playbook 3 (free PDF)
- Free companion material and the book series that covers the full methodology cleanly.
- TryHackMe
- Guided rooms for learning offensive and defensive security, with explanations built in.
- Unicorn — CPU emulator engine
- Emulate individual CPU instructions, not whole machines. Ideal for shellcode analysis.
- YARA — pattern matching for malware
- Free, open-source tool for identifying file families by byte patterns. Widely used professionally.
Mobile & Android Hacking
- androguard
- A Python toolkit for static and dynamic APK analysis. Scriptable, which makes it good for scanning many apps.
- Android Debug Bridge
- The core command line tool. Learn adb shell, logcat and the network commands properly.
- Android Open Source Project
- The platform source and documentation. Reading AOSP is the definitive answer to how Android really behaves.
- Android Security Bulletins
- Every monthly Android security patch note. The primary reference for which CVE affects which build.
- APKiD — packer and obfuscation detection
- Identifies packers, protectors and obfuscators in an APK, which tells you how much effort analysis will take.
- Apktool — APK disassembly and rebuild
- Decodes resources, smali and the manifest, then rebuilds a working APK. Essential for manifest and resource analysis.
- drozer — Android attack surface mapping
- Enumerates the exported components of an app and tests them for privilege issues. The most systematic way to audit IPC.
- Frida — dynamic instrumentation
- Inject JavaScript and native code into a running app on your own device. The essential tool for mobile reverse engineering.
- Frida documentation site
- Guides for hooking, bypassing integrity checks and inspecting traffic from inside a live process.
- frida-tools — the command line tools
- frida, frida-ps, frida-trace and friends. The workflow you will use every single session.
- jadx — dex to Java decompiler
- Decompiles an APK to readable Java with a GUI and searchable source. The first tool you reach for.
- LSPosed — Xposed framework for modern Android
- A maintained Xposed-style hook framework using Magisk. How you apply behaviour changes without repackaging an app.
- Magisk — systemless root
- Patches the boot image rather than the system partition, so it leaves almost no trace. Essential for instrumentation work on a real device.
- MobSF — mobile security framework
- Automated static and dynamic analysis of APKs and IPAs with a web UI. Excellent for a first pass.
- objection — Frida wrapper
- Automates the tedious parts of Frida: SSL pinning bypass, root detection bypass, keystore and file inspection.
- OWASP Mobile Application Security Testing Guide
- The free, open standard methodology for testing mobile apps, with platform-specific checklists and lab guides.
- OWASP Mobile Top 10
- The short version: the ten mobile flaws that actually matter. Start here, then move to MAS.
- Quark Engine — automatic app analysis
- Scripted Frida-based behavioural analysis of an app. Good for triaging many samples quickly.
- smali and baksmali
- The assembler and disassembler for Dalvik bytecode. Read smali when decompiled Java is ambiguous.
- Wireshark Bluetooth dissectors
- Decodes Bluetooth and BLE traffic in captures, which pairs well with an nRF52 sniffer.
Security Hats & Teams
- BloodHound
- Maps Active Directory relationships to expose privilege escalation paths. Standard for authorised AD assessments.
- Bug bounty programmes
- The directory of public bug bounty programmes, for testing systems whose owners have explicitly invited it.
- Center for Internet Security benchmarks
- Consensus configuration benchmarks for every platform. Free, and the practical output of hardening work.
- Certified Ethical Hacker (CEH) study resources
- ISACA's materials on information security governance, which is the part most offensive-only training skips.
- Cortex — analyser orchestrator
- Runs analysers against observables and returns results, paired with TheHive.
- CREST security accreditation
- The professional standards body for penetration testing, with the methodology documents free to read.
- CTFtime
- Capture the flag competitions, and a calendar of upcoming ones. The most legitimate way to practise offensive work.
- Impacket
- Python classes for Windows network protocols. The reference for SMB, LDAP and Kerberos on your own lab.
- Mythic — C2 framework
- A modular, actively maintained C2 with a web UI. Popular in authorised red team work.
- osquery
- Query a fleet of machines with SQL. The most practical endpoint visibility tool there is.
- Plaso (log2timeline)
- Forensic timeline generation from disk images. Unstaggering since 2012, and extremely thorough.
- pypykatz — Mimikatz in Python
- Credential extraction implemented in readable Python. Read it to understand the Windows credential model.
- Red Team Toolkit
- An open-source collection of the tools a red team reaches for, with a real information architecture behind it.
- Sigma — detection rules
- A generic signature format for SIEM rules, with thousands of community rules. The blue team's counterpart to a red technique.
- The hacker hat taxonomy
- White, grey and black hats as originally defined, plus the ethical code they all share. Read the history, not just the labels.
- TheHive
- An open-source case management platform for security operations. The centre of most small SOCs.
- Velociraptor
- An open-source DFIR and endpoint response platform written in Go, with a real query language.
- White hat
- Authorised testing, bug bounty work, and the disclosure norms that come with it.
- YARA rules repository
- Thousands of community detection rules. Free, well organised, and the place to learn pattern matching.
Nutrition & Health
Health
- APA — Psychology
- Free topic summaries of psychology research from the American Psychological Association.
- CCI — workbooks
- Free evidence-based workbooks for depression, anxiety, sleep and worry.
- Centre for Clinical Interventions (CCI)
- Free government workbooks for depression, anxiety, sleep, panic. Excellent.
- Coursera — free health courses
- Free audit tracks in medicine, nutrition, public health and epidemiology.
- COVID-19 — WHO guidance
- Free, current global health guidance hub. Useful example of a live health resource.
- FutureLearn — health
- Free health and wellbeing courses from universities. Short and good.
- Global Health Observatory (WHO)
- Free WHO data on health indicators for every country. Downloadable.
- HealthData.gov
- Free US health datasets from the government. Open, downloadable.
- IHME — Global Burden of Disease
- Free interactive tool for disease burden, risk factors and health trends.
- Mental Health Foundation (UK)
- Free information and research on mental health, wellbeing and stigma.
- Mindfulness-Based Stress Reduction (UW)
- Free MBSR course and information from the original programme. Evidence-based.
- NCCIH — health evidence
- Free NIH evaluations of supplements, complementary medicine and health claims.
- NHS — Every Mind Matters
- Free NHS mental health information, self-help and local services. Trustworthy.
- Nutrition & Physical activity (WHO)
- Free WHO guidance on physical activity and sedentary behaviour.
- NutritionData — free data
- Free food composition lookup from the USDA. Reliable numbers.
- Our World in Data — mental health
- Free, best-in-class data on mental health worldwide.
- Sleep Foundation
- Free, evidence-based sleep information. Practical and clear.
- The Conversation — Health
- Free expert commentary on health topics, written by academics.
- WHO — fact sheets
- Free, plain-language fact sheets on every major health topic.
Nutrition
- Academy of Nutrition and Dietetics
- The professional body for dietitians. Public articles and evidence free.
- BCcampus — Nutrition textbook
- Free open nutrition textbook from BCcampus. Peer-reviewed and free.
- Bristol chemistry teaching
- Free chemistry and food science school materials from the University of Bristol.
- Codex Alimentarius (FAO/WHO)
- The international food standards. Free, and the reference for food regulation.
- Dietary Guidelines for Americans
- The official US dietary guidelines. Free, evidence-based, every 5 years.
- EFSA — European Food Safety Authority
- Free European scientific opinions on food safety and nutrition.
- EFSA Journal — free
- Free EFSA scientific opinions on nutrients, contaminants and food safety.
- EU Food Information to Consumers
- Free EU reference on nutrition and health claims. Very useful for reading labels.
- EuroFIR — food composition
- European food composition databases and the FIRENE reference. Free data.
- FDA — food labeling & nutrition
- How to read nutrition labels, plus food safety and additives guidance. Free.
- Food Standards Agency (UK)
- Free UK food safety and nutrition guidance, including traffic-light labelling.
- FoodData Central API
- Free API into the USDA food database. Use it in your own tools.
- Harvard Nutrition Source
- Evidence-based nutrition articles. The plain-language ones are free.
- Healthy People — nutrition
- Free US Office of Disease Prevention nutrition guidance and resources.
- MDPI — Nutrients journal
- Fully open access nutrition research journal. Free to read in full.
- MyPlate
- USDA's official food guide: what to eat, how much. Free and visual.
- MyPlate — food groups explained
- Free explanation of the plate model, with what counts as a serving.
- National Agricultural Library (NAL)
- The USDA's nutrition and agriculture information centre. Free research access.
- NIDDK — nutrition and health
- Free authoritative information on nutrition, weight and metabolic health.
- Nutrition Evidence Library (USDA)
- Free systematic reviews of nutrition research. Rigorous evidence base.
- Nutrition.gov
- US federal nutrition information hub, backed by real databases. Free.
- Open Food Facts
- Open database of millions of food products with nutrition data. Fully open, downloadable.
- Open Food Facts data export
- Free bulk data dumps of millions of food products. Fully open.
- Spoon Foundation food education
- Free food-science education material for schools and students.
- Sustainable diets database
- Free peer-reviewed sustainable diet scenarios. Interesting research resource.
- USDA — MyPlate Kitchen
- Free budget-friendly recipes aligned to the dietary guidelines.
- USDA FoodData Central
- The official US food composition database and API. Free and authoritative.
- WHO — healthy diet guidelines
- Free WHO fact sheet on healthy diets. Short, clear, citable.
- WHO — Nutrition
- Free WHO guidance on nutrition, malnutrition and healthy diets globally.
- Wolfram Alpha — nutrition
- Free (with limits) nutritional analysis of foods and nutrients.
Sports nutrition
- Amino acid
- The twenty, their classification, and the essential ones the body cannot make.
- Australian Institute of Sport — supplements
- The Group A, B and C supplement framework. The most practical evidence grading available to an athlete.
- Bicarbonate
- Sodium bicarbonate loading, the buffering mechanism, and the GI cost of using it.
- Branched-chain amino acids
- Leucine, isoleucine, valine, and the evidence for and against supplementation.
- Caffeine
- Mechanism, dose-response, tolerance, and the genuinely useful performance data.
- Carbohydrate
- The macronutrient that rates exercise capacity more than any other.
- Creatine
- The most evidence-backed sports supplement there is, and the saturation protocol and safety data.
- Dietary fiber
- The fraction that matters for gut health, and the timing problem it creates around training.
- Electrolyte
- Sodium, potassium, chloride and magnesium, and what sweat rate actually tells you to take.
- Fatty acid
- Saturated, mono and poly, and what the evidence supports for performance.
- Glycogen
- The fuel store, its depletion, its supercompensation, and why tapering carbs before a long event works.
- Hydration
- Fluid balance, sweat rate, and the difference between drinking to thirst and drinking to a plan.
- Micronutrient
- Vitamins and minerals together, and why deficiency is common even in well-fed populations.
- Mineral (nutrition)
- The essential minerals, their roles, and the ones athletes are actually short of.
- Pre-workout
- The common ingredients and the caffeine evidence, which is the only well-supported one.
- Protein
- Structure and function, and why the debate about how much an athlete needs was oversimplified.
- Sports drink
- Carbohydrate-electrolyte solutions, the gastric emptying constraint, and when they help.
- Sports nutrition
- The field, and the three questions it actually asks: what to eat, when, and how much.
- Thermic effect of food
- The energy cost of digesting food, and why TDEE calculations are less certain than they look.
- Vitamin
- Fat-soluble and water-soluble, the deficiency and toxicity boundaries, and supplementation evidence.
Keyboards & Customization
Keyboard Switches & Parts
- Alps Alpine
- The Alpine switch, prized for its tactile bump and distinct sound. Worth trying next to an MX.
- Buckling spring
- The Model M mechanism, and why its sound and feel are unrepeatable in a custom board.
- Cherry MX switches
- The switch that made custom keyboards possible, and the company behind the MX profile and keycap standard.
- Hall effect sensor
- The sensing principle behind contactless switches and adjustable-actuation boards. The modern direction.
- Key switch (mechanism overview)
- Every switch technology in one article: membrane, dome, buckling spring, Hall effect, capacitive.
- Keycap
- Profiles, materials and doubleshot versus dye-sublimation printing. The thing most newcomers most want explained.
- Lubrication (for switches and stabilisers)
- The theory behind lubing. 205g0 on housings, thin oil on the stem, never both.
- macrolev — open source analog keyboard
- Analog keyboard position sensing. The most experimental hardware in the open-source keyboard world.
- Membrane keyboard
- The cheapest and most common technology, and why it feels the way it does.
- Model M keyboard
- The buckling spring board, its variants, and the restoration guides that go with them.
- Oryx
- An early capacitive keyboard, and the mechanism the BBC Micro used. Interesting for the history.
- Soldering
- The skill that gates most keyboard building. Through-hole versus hot air, and technique.
- Stabilizer (keyboard)
- Why the spacebar rattles, and the difference between plate-mount, screw-in and PCB-mount stabilizers.
- Through-hole technology
- The mounting style most custom keyboards use, because it lets you swap switches.
- Topre
- The electrostatic capacitive mechanism behind Realforce and HHKB. A completely different feel and sound.
- void_switch — Hall effect keyboard PCB
- Open-source KiCad files for a Hall effect switch board with adjustable actuation and rapid trigger.
Keyboards & Customization
- 1upkeyboards
- Open-source 60% and 40% designs, sold as kits and assembled. Excellent for a first build.
- Alchemist
- Keycap sets and deskmats, with unusually good photography. A good way to understand keycap profiles.
- C-13X — a handwired design
- A complete handwired Alice-layout board with schematic, PCB and case files. A good first non-rectangular build.
- Can I Use Vial?
- A compatibility list showing exactly which commercial keyboards support VIA. Saves buying the wrong board.
- CannonKeys
- US vendor, very strong on switches, keycaps and open-source board kits. Their switch sample packs are a good way to compare.
- Colemak
- A layout that changes far fewer keys from QWERTY while claiming better ergonomics. The best documented alternative.
- Deskthority wiki
- Encyclopedic reference on switch mechanisms, keycap profiles and case materials. The best single reference on the web.
- Drop
- Keyboards, keycaps and switches, with detailed community reviews. Useful for comparing before buying.
- Dvorak keyboard layout
- The most researched alternative layout, with the original finger-frequency study. Still worth reading.
- Ergohaven
- Open-source ergonomic keyboard designs with full files. The reference point for split ergo hardware.
- Ergonomic keyboard
- Split, tented, column-staggered and the evidence for and against each. Read before buying an ergo board.
- Handwired keyboard designs
- Free, complete build guides for a large range of handwired boards. The best way to learn what a keyboard physically is.
- HSKB — open-source HHKB-layout board
- A 60% board in HHKB layout, in KiCad. A clean reference design for a real custom PCB.
- Input Club
- Keycap sets and desk accessories from a community-focused brand.
- KBDFans
- A very large catalog of switches, keycaps and parts, with real stock data rather than preorders.
- Keebwerk
- Group buys and in-stock ergonomic kits, with clear timelines and good build documentation.
- Key rollover
- Why cheap keyboards drop keystrokes, and what n-key rollover actually means. Explains a lot of user complaints.
- Keyberon
- A pure-Rust firmware framework for split and ortho boards, with layouts in a Rust-like DSL.
- Keyberon firmware for STM32F4
- Keyberon on the STM32F401, the most common controller in DIY split keyboards.
- Keyboard layout
- ANSI versus ISO, layers, modifiers and the regional differences that matter when buying a case.
- Keyboard technology (Marshall)
- A long-running reference site on switch mechanisms and keyboard history, with clear technical explanations.
- Keyboard technology (overview)
- The full range, from membrane and rubber dome to buckling spring and Hall effect.
- Keychron
- Prebuilt boards, most QMK-compatible for remapping via Vial. The usual starting point for a first custom board.
- KMK firmware
- Python firmware for microcontrollers. You can write a keymap in Python, which makes complex logic tractable.
- MX-Alps hybrid footprint library
- KiCad footprints for boards that accept both Cherry MX and Alps switches. Rare, clever, and well documented.
- NovelKeys
- A long-running US vendor with deep technical detail on switches, keycaps and cases. Their switch guides are the reference.
- QMK documentation
- Keymap syntax, layers, combos, tapping behaviour and the full reference. Read the 'Understanding QMK' section first.
- QMK firmware
- The dominant open-source keyboard firmware. Virtually every custom board runs it, and the docs are excellent.
- QMK Toolbox
- The official GUI for compiling and flashing QMK. Removes the command line from the first build.
- r/MechanicalKeyboards wiki
- A genuinely good community wiki on terminology, sizes and buying advice. Surprisingly well written.
- Rama Works
- Machined aluminium boards with unusually good documentation. Expensive, and worth reading about regardless.
- SoundTested — switch sound library
- A large library of switch, case and keycap sound recordings. The only way to compare sound before buying.
- Vial — graphical keymap configurator
- Remap keys in a browser instead of recompiling firmware. The change that opened the hobby to non-programmers.
- ZMK documentation
- Device tree configuration, power management and shield listings. Well organised and complete.
- ZMK firmware
- The modern alternative to QMK, built for wireless and low-power boards. The power management is far better.
Medicine
Medicine
- Allergies — free clinical reference
- Free NIAID information on immune disorders, allergies and infectious disease.
- Anaesthesia UK
- Free anaesthesia teaching material and exam questions. Very good.
- Anki — spaced repetition
- Free open-source flashcard SRS. The most effective way to learn medicine.
- Anki manual and docs
- Official Anki documentation and deck-sharing guidance. Free.
- AnKing medical decks
- Free, high-quality, community-maintained Anki decks for the whole medical curriculum.
- Antimicrobial Resistance (WHO)
- Free authoritative global resource on AMR. Current and important.
- BMC Medicine
- Open access clinical journal. All articles free.
- BMJ — open content
- BMJ research, news and guidelines. Much of the content is now free.
- BMJ Case Reports
- Free open access case reports across all specialties. Great for learning.
- CDC — Centers for Disease Control
- Free, trusted public health guidance, disease data and travel advice.
- ClinicalTrials.gov
- Registry of every clinical trial worldwide. Free, searchable, current.
- Cochrane — plain language summaries
- Free patient-friendly summaries of the best medical evidence.
- Cochrane Library
- The gold standard of systematic reviews. Abstracts free, many full reviews open.
- Deranged Physiology
- Free, beautifully illustrated physiology made genuinely fun. Essential for understanding.
- ECDC — European CDC
- Free European public health surveillance and guidance.
- EMA — European Medicines Agency
- European drug regulation and safety. Free.
- Emedicine / Medscape
- Free reference articles on conditions across specialties. Good depth.
- eReferral / telemedicine resources
- Free HHS resource on telehealth policy and practice. Current.
- FDA — Food and Drug Administration
- Drug approvals, safety warnings, recalls. Free and authoritative.
- Geeky Medics
- Free OSCE revision guides for every specialty. Clear, systematic, well illustrated.
- IDSA Guidelines (free)
- Free infectious disease clinical practice guidelines from a major society.
- Life in the Fast Lane (LITFL)
- Free, hugely popular clinical reference: ECG, ICU, emergency, procedures. Outstanding.
- LOINC — free database
- Free, the global standard identifiers for tests and observations. Downloadable.
- Meddean
- Free open-access medical education: cases, questions and learning resources.
- MedlinePlus
- NIH patient and family health information. Free, plain language, trustworthy.
- Merck Manual — Consumer
- Free plain-language health information for the public.
- Merck Manual — Professional
- Free, comprehensive medical reference for clinicians. Excellent and free.
- Million Hearts (CDC)
- Free clinical resources and tools for cardiovascular disease prevention.
- NEJM Images in Clinical Medicine
- Free clinical images with expert commentary. Superb for pattern recognition.
- NICE guidelines
- Free UK clinical guidelines. Rigorous, evidence-graded, very usable.
- NINDS — stroke and brain health
- Free NIH resource on the brain, stroke, pain and neurological disease.
- NLM Clinical Table Search Service
- Free structured clinical vocabularies: medications, conditions, labs. US government.
- NLM Digital Collections
- Free historical medical images, posters and texts from the US National Library of Medicine.
- NYSORA — anaesthesia
- Free, illustrated reference on regional anaesthesia and nerve blocks. Excellent.
- Open-i — biomedical image search
- Free search engine for open access biomedical figures and images. Very useful.
- OpenWHO
- Free WHO online courses on public health, epidemics and emergencies. Official.
- PLOS Medicine
- Fully open access global health journal. Free to read in full.
- Radiology Masterclass
- Free tutorials on radiology interpretation with sample images. Excellent.
- Rare diseases (Orphanet)
- Free international database on rare diseases and expert centres. Unique resource.
- SNOMED CT
- The largest clinical terminology system in the world. Free to browse.
- StatPearls — main collection
- The StatPearls collection: concise, peer-reviewed, free chapters on every topic.
- The Lancet — free content
- Flagship clinical journal. Some content free, and much is on ResearchGate-free.
- The Radiology Assistant
- Free, detailed radiology tutorials by a radiologist. Very high quality.
- USPSTF recommendations
- Free US preventive-care screening recommendations. Highly useful and clear.
- Visible Human Project (NLM)
- Free cross-sectional images of the whole human body from the NLM. Extraordinary.
- Wellcome Collection — health library
- Free digital library of health and medicine books, manuscripts and films.
- WHO — International Classification of Diseases
- Free ICD coding resources. The global standard for diagnosis classification.
- WikEM (Emergency Medicine)
- Free, community-edited emergency medicine wiki. Practical checklists.
- World Health Organization
- Global health guidelines, fact sheets, statistics. Authoritative and free.
Sport, Fitness & Performance
Muscles
- Acetylcholine
- The transmitter at the neuromuscular junction, and its much broader role in the nervous system.
- Actin
- F-actin and G-actin, polymerisation, and why it is the jack in the cross-bridge cycle.
- Bioenergetic systems
- Phosphagen, glycolytic and oxidative systems, their capacities and recovery times. The core of training-zone design.
- Cartilage
- Avascular, almost no metabolic support, and why articular cartilage problems are slow and hard.
- Collagen
- The structure of tendon, ligament and skin, and how training remodels it.
- Connective tissue
- The supporting framework, and the passive tension that soft-tissue work manipulates.
- Dystrophin
- The protein whose absence causes Duchenne muscular dystrophy, and the cytoskeleton link it forms.
- Electromyography
- Measuring muscle activation electrically, and what the signal can and cannot tell you about force.
- Hemoglobin
- Cooperativity, the Bohr effect, and why altitude training changes it.
- Ligament
- Bone to bone, with the viscoelastic behaviour that explains injury and rehabilitation timing.
- Motor unit
- One motor neuron and the fibres it innervates. The unit of recruitment and rate coding, and therefore of force control.
- Muscle
- The three muscle types, how they differ, and the organisation from fibre to whole muscle.
- Muscle architecture
- Pennate versus parallel, fibre length and pennation angle, and why they set maximum force.
- Muscle atrophy
- The pathways involved, and how quickly disuse starts reversing months of work.
- Muscle cell
- The muscle fibre as a cell, its multinucleation, and the myoblast fusion process.
- Muscle contraction
- Excitation-contraction coupling end to end, from a nerve impulse to shortening.
- Muscle fibre
- Type I and type II, the fast subtypes, and why the ratio predicts sport more than strength does.
- Muscle hypertrophy
- Adding contractile protein to a fibre, and why it is a slow process that most training barely triggers.
- Muscle spindle
- The receptor that measures muscle length and sets the stretch reflex. The Golgi tendon organ is its counterpart for tension.
- Myosin
- The motor protein, its isoforms, and the ATPase that makes contraction reversible.
- Myostatin
- The negative regulator of muscle growth, and why blocking it is the most interesting bad idea in the field.
- Neuromuscular junction
- The synapse that transmits every voluntary command, and why it is the first thing affected in fatigue.
- Pennate muscle
- The architecture that trades shortening velocity for force, and why it dominates in the quadriceps.
- Sarcomere
- The contractile unit. The Z-line to Z-line distance is the practical measure of contraction.
- Sarcopenia
- Age-related muscle loss, its diagnosis, and the resistance training that actually slows it.
- Satellite cell
- The resident stem cell that supplies nuclei for new fibres during hypertrophy. The current mechanistic story for why muscle grows.
- Skeletal muscle
- Fibre types, fascicle structure, and the architecture that determines force and speed.
- Sliding filament theory
- The mechanism that replaced the old model, and the cross-bridge cycle underneath it.
- Striated muscle tissue
- Skeletal and cardiac muscle, the banding, and the satellite-cell biology that differs between them.
- Tendon
- How tendons transmit force, and why they adapt to load far more slowly than muscle does.
- Titin
- The giant elastic protein that acts as a spring and is the main passive element in muscle.
Sports medicine & Injuries
- Agility
- Change-of-direction ability, how it differs from speed, and how to train it.
- Ankle sprain
- The most common sports injury there is, and the high rate of chronic instability left untreated.
- Anterior cruciate ligament
- The anatomy and function, and why it is the most studied ligament in sport.
- Anterior cruciate ligament injury
- Mechanism, the graft options, and the return-to-sport timeline that is still routinely overoptimistic.
- Blood flow
- Perfusion, its restriction during lifting, and the growth stimulus argument around it.
- Concussions in sport
- Return-to-play protocols, and the accumulating concern about cumulative head impact.
- Dehydration
- Heat illness risk, plasma volume change, and the cost of dehydration to performance.
- Dry needling
- The technique, and the evidence picture — which is far weaker than the clinic marketing.
- Heat exhaustion
- Recognition and first response, and the difference from heat stroke.
- Hypothermia
- Cold injury in sport, from water immersion in open water to alpine exposure.
- Musculoskeletal injury
- Overuse versus acute, the mechanism split, and why the two need opposite management.
- Occupational therapy
- Rehabilitation and return-to-function, the other half of injury management.
- Osteopathy
- The discipline, and the ongoing debate about the evidence base.
- Overtraining syndrome
- The non-functional overreaching to syndrome progression, and the diagnostic problem in between.
- Physical therapy
- The profession, its methods, and the specialism in sport and orthopaedics.
- Plantar fasciitis
- The classic running overuse injury, and the loading-based rather than rest-based management.
- Prehabilitation
- Preparing tissue before it is damaged. The best-evidenced idea in injury prevention, and free to add.
- Range of motion
- How flexibility is actually measured, and the reference ranges for major joints.
- Rotator cuff
- The four muscles, their roles, and the impingement and tear patterns that follow from throwing.
- Sports medicine
- The field, from the first sports physicians to multidisciplinary team sport.
- StatPearls — sports medicine
- Free peer-reviewed clinical summaries, and the most useful single reference for any injury or condition you need to look up.
- Stress fracture
- Fatigue versus insufficiency fractures, and why bones need load to stay strong.
- Stretching
- The evidence review, and why it reframed warm-ups and injury prevention entirely.
- Tendinopathy
- The load-capacity model that replaced the inflammation model, and it changes the treatment.
Sports science
- Aerobic exercise
- The oxidative pathway, its adaptations, and the dose-response that actually holds.
- American College of Sports Medicine
- Position stands on exercise testing, prescription and nutrition. The reference for what the profession actually recommends.
- Anaerobic exercise
- Alactic and glycolytic work, and the severe limits both run into quickly.
- BASES
- The British Association of Sport and Exercise Sciences. Research summaries and position statements.
- Bioenergetics
- Energy transduction in cells, which is the metabolic layer underneath every training adaptation.
- Biomechanics
- Statics, dynamics and kinetics applied to movement, and the analysis methods each implies.
- Body Physics 2.0 (open textbook)
- Free physics text built around the human body, and an unusually good introduction to biomechanics and body composition.
- Delayed onset muscle soreness
- The mechanism is now reasonably settled, and it is not what most people assume.
- Doping
- The practice, the pharmacology, and the arguments on both sides of the line.
- EPOC
- Excess post-exercise oxygen consumption, and why hard intervals can help aerobic fitness when steady work does not.
- Exercise
- The general case, and the distinction from physical activity and from sport.
- Exercise Delivery (open textbook)
- A free CC-licensed text on delivering exercises and programming them, with videos per muscle group. The most directly useful sport-science textbook that is actually free.
- Expected goals
- The metric that replaced raw shot counts, and the reason it spread so fast.
- Fitts's law
- The index of difficulty relating distance to target size. Still the most useful law in motor control for sport.
- Frontiers in Physiology
- Open-access physiology, including a large exercise and sports section.
- Human Kinetics OER guide
- A curated map of open human kinetics resources, which is useful for finding the rest.
- International Society of Sports Nutrition
- The body behind the ISSN position stands, which are the most-read free reference documents in sports nutrition.
- ISSN journal
- The peer-reviewed journal of the ISSN, free to read, and where the position stands are published.
- Journal of Sports Science & Medicine
- Free full text on sports medicine, training and physiology. The best open journal in the field by a wide margin.
- Kinesiology
- Human movement as a subject, and the study of its causes and consequences.
- Lactate
- What it is, what it is not, and the accumulated evidence that it is not the cause of fatigue.
- Motor control
- How the nervous system turns intent into coordinated movement.
- Motor learning
- How skills are acquired and retained, and why practice conditions matter more than practice volume.
- Open Sport
- A free journal on sport sciences, psychology and pedagogy.
- Placebo
- The control condition in every trial, and a surprisingly large effect size in sport science.
- PLOS ONE
- Open-access primary research with a sound editorial standard and no author fees.
- Sabermetrics
- Where quantitative analysis of sport came from, and the epistemics it has to answer for.
- Second wind
- The shift from glycolytic to oxidative fuelling, and the unpleasant gap it creates.
- Sports Medicine — Open
- Open-access sports medicine and exercise science. Peer reviewed and entirely free to read.
- Sports science
- The interdisciplinary field, and the physiology, biomechanics and psychology inside it.
- VO2 max
- The most-cited fitness measure in the world, and what it does and does not predict.
- World Anti-Doping Agency
- The rules, the prohibited list, and the testing regime that enforces them.
- World Athletics
- The governing body for track and field, with rules, rankings and the competition data.
Strength & Conditioning
- Barbell Medicine
- Strength training through a physiotherapy lens, with real client case studies and published research.
- Bench press
- The press, its variants, and the shoulder problems that come from chasing numbers.
- Calisthenics
- Bodyweight training and progressions, and honestly assessing the limits it has.
- CrossFit
- What it actually is, where it came from, and the evidence base underneath it.
- Deadlift
- Variants, technique, and why it is the test most people should not run un coached.
- Dynamic stretching
- Movement-based preparation, and the better evidence base compared with static work.
- Foam rolling
- What self-myofascial release plausibly does, which is less than the marketing claims.
- Hypertrophy
- Muscle growth as a training goal, with the load, volume and frequency evidence.
- Myofascial release
- The manual technique, and the thin evidence under a very large market.
- Olympic weightlifting
- Snatch and clean and jerk, the two lifts that made modern strength training.
- Plyometrics
- Stretch-shortening cycle work, the specificity of the adaptation, and how easily it turns into injury.
- Powerlifting
- The competition, its federation differences, and how far it is from general training.
- Progressive overload
- The one principle everything else depends on, and the many ways it is faked.
- Sports periodization
- Planned variation across the season, and the history of why it replaced linear training.
- Squat
- Technique, anatomy, depth debates and the loading history. The most argued-over lift in the sport.
- Static stretching
- The technique, and the well-replicated finding that it does not prevent injury.
- Strength training
- The whole discipline, its terminology, and the principles the rest of the category hangs off.
- Stronger by Science
- Greg Nuckols and the group. The most methodologically careful strength research site that is free to read.
- Supercompensation
- The recovery-adaptation model that periodisation is built on, in both its simple and its honest form.
Tennis
- Angular momentum
- Why racket head speed and release point matter, and how a ball is actually spun.
- Arthur Ashe
- The first Black man to win a major, and a career that was also a civil rights story.
- ATP rankings
- How points accumulate, and why the ranking system is a partial and contested measure.
- ATP Tour
- The men's professional tour, its ranking system and its calendar structure.
- Australian Open
- The January major, its hard courts and its move to a faster surface.
- Australian Open official site
- Scores, draw and the Australian summer major.
- Backhand
- One-handed and two-handed, and the trade each makes.
- Ball spin
- The aerodynamic effect behind sidespin, topspin and the whole modern serve.
- Billie Jean King
- The player and the figure behind equal prize money and the Battle of the Sexes.
- Bouncing ball
- The physics of the bounce, and why the coefficient of restitution decides how a court plays.
- Centre of mass
- The basis of balance, recovery and shot stability, and what separates a good mover from a strong one.
- Coefficient of restitution
- Why the ball leaves the strings with more energy than it arrived with, and what that costs you.
- Davis Cup
- National team competition, the oldest event in the sport, and its decline.
- Doping in tennis
- The documented cases and the testing regime, and how the sport has handled it.
- Federer–Nadal rivalry
- The most analysed match-up in the sport, and what made it a real rivalry rather than a style contrast.
- Forehand
- Technique, the continental-versus-modern grip argument, and flat versus heavy topspin.
- French Open
- Roland-Garros, the clay, and the endurance test that sets it apart.
- Glossary of tennis terms
- The vocabulary, including the jargon that a serious player needs to follow coverage.
- Grand Slam (tennis)
- The four majors, the calendar, and the different surfaces and scoring traditions.
- Hard court
- Asphalt and acrylic surfaces, and the middle ground they occupy between grass and clay.
- Hawk-Eye
- The camera system that made line calling reviewable, and the accuracy research behind it.
- International Tennis Hall of Fame
- The institutional record of the sport and where to find primary material on it.
- ITF
- The governing body, its rules of tennis, and how the rulebook is maintained.
- ITF — coaching
- The ITF coaching education pathway, and the reference points it uses.
- ITF — player development
- Coaching, technical and physical development resources from the governing body.
- ITF — rules of tennis
- The official rulebook. The single source for anything about how a match actually works.
- Love (tennis)
- The origin of the word, and the scoring in a game with a player scoring nothing.
- Multi-stage tournament
- How slams, Masters and ATP 250 to 1000 events are actually structured.
- Pressure (physics)
- Ball pressure, string tension, and the trade between power, control and feel.
- Racket (sports equipment)
- String materials, frame stiffness and the physics of the sweet spot.
- Rafael Nadal
- The clay court record and the physical game behind it.
- Roger Federer
- The reference point for the modern game, and the closest thing to a career masterclass.
- Roland-Garros official site
- The French Open, and the clay-court draw and results.
- Serena Williams
- The most dominant player in the sport's history, by a considerable margin.
- Serve (tennis)
- The toss, the trophy position, pronation, and the serve as a whole-body kinetic chain.
- Shoulder
- The joint that generates and absorbs nearly all of the racket speed, and the site of most tennis overuse injury.
- Sidespin
- What the sidespin on a slice or a kick serve actually does to the bounce.
- Tennis
- The sport from the top: origins, the four majors, scoring, surfaces and equipment.
- Tennis ball
- Felt, fuzz, pressure and the bounce standard that makes surfaces comparable.
- Tennis court
- Dimensions, the net height rule, and how court speed follows from the surface.
- Tennis Hall of Fame — official site
- The institution itself, with the museum and the primary collection.
- Tennis racket
- Head size, weight, balance and swingweight, and what each does to the ball.
- Tennis scoring system
- 15-30-40, deuce and advantage, and why the whole scheme exists.
- Tennis strategy
- Serve-plus-one, return position, targeting and the patterns that actually decide points.
- Tiebreak
- The scoring rules, the history of when it is used, and how it changes match dynamics.
- Topspin
- The shot that changed tennis, and the physics of the dip it puts on the bounce.
- Torque
- The rotational quantity behind every stroke. The physics of where power actually comes from.
- US Open (tennis)
- The first of the modern majors, and the site that built the sport in America.
- US Open official site
- Scores and statistics from the hard-court major.
- USTA
- The US governing body, with rules, player development and the magazine.
- Wimbledon Championships
- The oldest major, the grass, and the traditions that make it distinct.
- Wimbledon official site
- Scores, draw, order of play and the grass-court data, updated live through the fortnight.
- WTA Tour
- The women's tour, and how the two tours differ in structure and in pay.
Telecommunications & Networking
Networking
- APNIC training and resources
- Free, well-structured courses on IP addressing, BGP, RPKI and network operations.
- ARP, and why it still matters
- The old layer 2-to-3 mapping, and why understanding it explains many local attacks.
- Bandwidth and latency explained
- Clear definitions of the terms that network monitoring tools report, and how they differ.
- Batfish — network configuration analysis
- Open-source tool that analyses network configs and answers reachability questions. Very powerful.
- BGP in a nutshell
- APNIC's blog has excellent free explainers on BGP, RPKI and routing security.
- BGP in the real world (Flockbox blog)
- APNIC's research team writes accessible explainers on real internet routing incidents.
- bgp.tools
- Free, fast BGP lookup and prefix explorer. Best way to understand who announces what.
- BIND 9 documentation (ISC)
- The reference open-source DNS server, with thorough authoritative documentation.
- BIRD Internet Routing Daemon
- Another excellent open-source routing daemon, smaller and very readable C code.
- Cilium — eBPF networking
- Open-source networking for Kubernetes using eBPF. Excellent free documentation.
- CISA networking and infrastructure guidance
- Free US government guidance on network security, scanning and critical infrastructure.
- Computer Networking: A Top-Down Approach (free notes)
- The best networking textbook, with free slides, readings and lecture videos. The place to start.
- CoreDNS and DNS service discovery
- The DNS server used inside Kubernetes clusters. Free plugin architecture worth reading.
- Cumulus Linux (NOS) documentation
- Open-source network OS built on Linux. Its documentation is a free, excellent networking course.
- DNS explained — Cloudflare learning centre
- Free, clear explanations of DNS, TLS and HTTP, with diagrams and practical detail.
- DNS root servers and operations
- How the DNS root system works, and who operates the thirteen root servers.
- Ethernet frame format (Wikipedia)
- The actual bytes on the wire, explained. Essential for reading a hex dump.
- FRRouting — open routing suite
- The open-source routing stack: BGP, OSPF, IS-IS. Read the code to learn how routers work.
- GNS3
- Graphical network emulation combining real virtual machines with virtual routers. Free and open source.
- GoBGP — BGP in Go
- A complete, modern BGP implementation in Go. Clean code, ideal for learning BGP internals.
- Hurricane Electric BGP toolkit
- Long-standing free tool for looking up prefixes, origins and AS relationships.
- IANA IPv4 special-purpose registry
- Every reserved IPv4 block, with references. Useful and precise reference data.
- Internet Society — technical reports
- Free reports on the technical and policy state of the internet.
- IP address allocation and registries
- The official registries for IPv4 and IPv6 address space. The authoritative source.
- iperf3
- Measure real TCP and UDP throughput. The standard bandwidth test between two hosts.
- IPv4 and IPv6 protocol specs
- The IPv6 specification, free, and noticeably more readable than the IPv4 RFC.
- Jitter, packet loss and QoS
- Why voice and video care about jitter more than bandwidth. Clear, practical explanation.
- Kurose & Ross — online resources
- Complete lecture video series and chapter resources for the top-down networking course.
- Linux kernel networking documentation
- The authoritative documentation for Linux networking internals, written by the maintainers.
- MANRS — secure internet routing
- The standard for operator security practices, with free, concrete guidance.
- Mininet — network emulation
- Create an entire virtual network of switches, routers and hosts from a Python script. Superb for learning.
- NetFlow and IPFIX
- The free standards behind flow-level network visibility. Learn this before touching monitoring tools.
- Network automation with Ansible
- Open-source network automation. Free modules cover most major network operating systems.
- Network namespaces in Linux
- Authoritative man page for network namespaces, the basis of container networking.
- Network performance measurement (RFC 6349)
- The free standard for measuring IP performance, written by the IETF.
- nftables and iptables documentation
- The modern Linux firewall. Clear wiki documentation with many worked examples.
- nmap
- Network discovery and port scanning. Free, open source, and the canonical security tool.
- nmap scripting engine (NSE)
- The free Nmap scripting manual. Automate discovery and enumeration with small Lua scripts.
- Open Networking Foundation
- The Linux Foundation's home for open networking projects and their documentation.
- OpenConfig models
- Vendor-neutral, open data models for configuring network devices. Free and well designed.
- Palo Alto Unit 42 threat research
- Free, detailed technical research on network and protocol attacks. Genuinely good writing.
- PeeringDB
- The public database of network interconnection points. Free and authoritative.
- Ping, ICMP and troubleshooting
- Clear explanation of how ping, traceroute and ICMP actually diagnose problems.
- QUIC transport protocol (RFC 9000)
- The modern encrypted transport running most web traffic. The spec is free and readable.
- RIPE NCC — Internet coordination
- The European Internet registry. Free routing data, statistics, measurement and training.
- RIPE NCC measurement data
- Free datasets on internet reachability, IPv6 deployment and DNS root servers.
- RIPE NCC training
- More free networking courses with detailed material on routing and the registry system.
- RIPE RIS Live — global routing data
- Free live BGP routing data from collectors worldwide. Analyse real internet routing.
- RIPEstat
- Free API for network measurements, routing statistics and looking up any prefix's history.
- RouteViews — routing data archive
- The longest-running public archive of internet routing data. Free and enormous.
- RPKI and route origin validation
- How cryptographic origin validation protects the routing system. Key modern BGP security topic.
- Scapy
- Python library for crafting and injecting arbitrary packets. The best way to truly understand a protocol.
- Scapy documentation
- Complete, well-written docs with recipes for building and parsing packets in Python.
- Spanning tree protocol
- The algorithm preventing layer 2 loops, and the cause of the classic broadcast storm.
- Subnetting and CIDR practice
- Free interactive tool for becoming genuinely fast at subnet calculation. Essential skill.
- tcpdump
- The classic command-line packet capture tool, present on every Linux system. Learn it well.
- TLS 1.3 specification (RFC 8446)
- How modern transport encryption actually works, specified precisely and freely.
- Tor design documentation
- The free design document explaining how Tor achieves anonymity. A serious protocol read.
- traceroute and mtr
- Path tracing tools for diagnosing routing problems. mtr continuously shows per-hop loss.
- Unbound DNS resolver
- A fast, secure, open-source validating DNS resolver. Excellent codebase to read.
- VLANs and switching fundamentals
- How virtual LANs separate traffic on shared physical infrastructure.
- Wireshark — the protocol analyser
- The free, open-source network protocol analyser. The single most useful networking tool.
- Wireshark display filter reference
- The official display filter guide, a genuinely useful reference written for humans.
- Wireshark sample captures
- Hundreds of real packet captures for every protocol imaginable. Ideal for learning offline.
- Wireshark wiki — protocol dissection notes
- Deep notes on how each protocol is dissected, with dissector source. Excellent for learning protocols.
Telecommunications
- 3GPP — cellular standards
- The body that writes 4G, 5G and beyond. All specifications are free to download. Start here for cellular.
- 3GPP specification portal (free download)
- Direct access to every 3GPP specification, free and without registration.
- 3GPP TS 23.501 — 5G system architecture
- The core 5G architecture specification. Dense, but it is the map of the whole system.
- Asterisk and FreeSWITCH telephony
- Open-source telephony platforms; their documentation doubles as a free telephony textbook.
- Dense WDM and optical networking
- How dozens of channels share one fibre, and why backbone bandwidth keeps climbing.
- ETSI — European Telecommunications Standards Institute
- Free downloadable standards including GSM, LTE and the full European rulebook.
- FCC spectrum management
- US spectrum allocation, licensing and the rules governing who may transmit what.
- Fibre optic technology explained
- Practical and theoretical fibre optics resources, from basic propagation to DWDM.
- GSMA — mobile industry association
- Mobile network specifications, roaming documentation and technical reports, many free.
- GSMA Open Gateway
- An open API for mobile network operators. Learn real carrier APIs.
- IANA — Service Name and Port Number Registry
- Free list of every assigned port number, useful when identifying traffic in a capture.
- IEEE 802 — LAN/MAN standards
- The Ethernet, Wi-Fi and bridged LAN standard family. Many are free to download.
- IEEE 802.3 Ethernet standard (free)
- The official Ethernet specification. Free through the IEEE GET Program.
- IEEE Communications Society
- Many free technical articles and tutorials on communications and networking.
- IETF — Internet Engineering Task Force
- Where the Internet is actually designed. All RFCs are free, and the mailing lists are readable.
- ITU — International Telecommunication Union
- Global telecom standards, radio regulations and free reference publications.
- ITU Radio Regulations (RR)
- The single international treaty defining the global radio frequency allocation table. Free download.
- ITU-T recommendations (free)
- The technical recommendations that define how telephone and data networks interconnect worldwide.
- MPLS and segment routing — IETF work
- A free RFC that explains segment routing properly. A good modern networking primer.
- NANPA — North American Numbering
- How telephone numbers are assigned and routed in North America. Free reference data.
- O-RAN SCREAM and open source RAN
- Open-source RAN components and test frameworks from the O-RAN alliance.
- Open RAN Alliance
- An open, vendor-neutral 5G radio access architecture, with published specifications and code.
- Optical transport: OTN and SDH
- The ITU standard for optical transport networks, the backbone under the internet.
- Public switched telephone network (PSTN) history
- How the telephone network evolved from manual switches to softwarised infrastructure.
- RFC index by number
- Browse the complete RFC catalogue. Many older RFCs read like tutorials.
- Roaming and numbering portability (ITU)
- Free ITU-T material on how calls and numbers move between operators and countries.
- SD-WAN and cloud networking
- Free IETF documents describing overlay networks, a good modern networking primer.
- SIP and VoIP tutorials
- Asterisk: a complete open-source telephony stack. Read the code to understand SIP end to end.
- Spectrum management tools (ITU)
- The Radio Regulations Bureau's official resources, including the allocation database.
- TIP Open RAN
- Telecom Infra Project: practical open RAN deployments with member-published designs.
- VoIP and SIP — RFC 3261
- The Session Initiation Protocol, free and readable. The foundation of internet calling.
- WebRTC — real-time communication
- Open, free specs and implementation notes for peer-to-peer audio and video in the browser.
- Wi-Fi Calling and VoLTE explained
- How voice calls hand over between the packet core and the circuit-switched fallback.
Atomic & Particles
Nuclear physics
- Alpha decay
- The Geiger-Nuttall law, the tunnelling explanation, and why alpha energy is a clock.
- Atomic nucleus
- Protons, neutrons, and the forces and radii that measurement has pinned down.
- Bertulani — books and lecture material
- The author's page for Nuclear Physics in a Nutshell, with related texts and course links.
- Beta decay
- Weak-interaction decay, the neutrino, and the parity violation that made it famous.
- Big Bang nucleosynthesis
- The first three minutes, and the observational evidence for them.
- Binding energy
- The mass deficit, why iron sits at the top of the curve, and where fusion gets its energy.
- Chain reaction
- Criticality, multiplication factor, and what actually has to be controlled.
- Chernobyl disaster
- What a RBMK design flaw and a disabled safety system actually produce.
- Critical mass
- Why the quantity that matters is shape and density, not just mass.
- Decay chain
- The series from a heavy parent down to a stable daughter, including the uranium and thorium series.
- Deuterium and tritium
- The two isotopes every fusion proposal on earth uses, and why.
- Diffusion equation
- The neutron transport equation in its simple limit, and how reactor codes actually solve it.
- Fukushima Daiichi accident
- Station blackout defeating both the reactors and the diesel backup. The case for passive safety.
- Gamma ray
- De-excitation radiation, the nuclear gamma cascade, and the metre-long range of the highest energies.
- Gamma ray burst
- The most energetic events in the universe, and what they say about massive star death.
- Geiger–Nuttall law
- The original evidence for quantum tunnelling, and the first nuclear physics that worked.
- Generation III reactor
- Passive safety designs, and why intrinsic feedback is better than active protection.
- Generation IV reactor
- The designs meant to use far less fuel and produce far less waste.
- IAEA LiveChart
- Interactive chart of nuclides with decay data and interactive facilities. Excellent for teaching.
- Integral fast reactor
- Breeding fuel and burning waste in the same core. The design the US funded and then stopped.
- Isotope
- What defines an isotope, and why some are stable, some are not, and some are useful.
- Kyshtym disaster
- The worst radiation release ever recorded, and almost nobody knows it happened.
- Lawrence Berkeley National Laboratory
- Isotope science and accelerator physics, with a large free report archive.
- Lawson criterion
- The break-even condition for fusion, derived from the confinement physics rather than guessed.
- Magic number (physics)
- The closed shells at 2, 8, 20, 28, 50, 82 and 126, and the evidence for them.
- Manhattan Project
- The programme, the people and the physics, and the decision to use the result.
- Mass–energy equivalence
- The mass defect that makes binding energy real, and the source of all nuclear energy.
- MOOSE
- Idaho's framework for coupled multiphysics simulation, including reactor and heat-transfer problems.
- Neutrino
- The particle that made beta decay work, and its own oscillation physics.
- Neutron
- Lifetime, magnetic moment, and the neutron beta decay experiment that fixed three constants at once.
- Neutron activation analysis
- Identify and quantify elements by making them radioactive. A genuinely useful nuclear technique.
- Neutron moderator
- The choice of moderator is what decides what kind of reactor you have built.
- Neutron poison
- Absorbers used for control, and why control rods work at all.
- Neutron star
- Degenerate matter under extreme pressure, and the only place the heaviest nuclei exist stably.
- NIST reference data
- Physical constants and measurements, including the fundamental particle masses.
- NNDC — ENSDF
- The Evaluated Nuclear Structure Data File. The primary source for every measured level and decay.
- NNDC — nuclear data
- Evaluated nuclear data, decay schemes and the reference values most of the field quotes.
- Nuclear astrophysics
- The field that connects the two, including the s-process and r-process.
- Nuclear cross section
- The central quantity of reactor physics, and the curve you look up for any isotope and reaction.
- Nuclear fission
- The mechanism, the energy release, the products, and the chain reaction it makes possible.
- Nuclear fusion
- Fusion from stellar nucleosynthesis to inertial confinement, and the enormous engineering difficulty.
- Nuclear isomer
- Metastable excited states, and why they store energy long enough to be harvested.
- Nuclear magnetic resonance
- The interaction that made MRI work, and that let you measure nuclear properties precisely.
- Nuclear physics
- The field overview, and a good map of what connects to what.
- Nuclear power
- How much of the world runs on it, and the arguments on both sides.
- Nuclear power in Finland
- The other outlier: near-total nuclear, a very good record, and strong public acceptance.
- Nuclear power in France
- The one country that took the nuclear option seriously, and what it cost. The most instructive case study there is.
- Nuclear reactor
- The full range of designs, and the physics each one is exploiting.
- Nuclear reactor safety system
- Redundancy, diversity, containment and negative reactivity coefficients, as engineering principles.
- Nuclear shell model
- Magic numbers, and why nuclei have a periodic table of their own.
- Nuclear weapon
- How the weapons work, the yield scales, and the delivery mechanisms.
- Nuclear weapon testing
- The test series, the yield diagnostics, and the treaties that followed them.
- Nucleosynthesis
- Building the elements in stars. The place nuclear physics and astronomy become the same subject.
- Oak Ridge National Laboratory
- Neutron science, isotopes and reactor engineering. Their public technical reports are excellent and free.
- Oklo
- Natural fission reactors, two billion years old. Proof the physics was always possible.
- OpenMC
- Open-source Monte Carlo particle transport, used for reactor and shielding physics. Free and serious.
- OpenMC documentation
- The user guide, with input syntax and worked examples you can actually run.
- Particle decay
- The general framework, lifetimes, and the free falloff rate that dates unstable particles.
- Proton
- Structure, spin, magnetic moment and the internal quark structure now measured.
- Quantum chromodynamics
- The gauge theory of the strong force, and why confinement and asymptotic freedom are hard to compute.
- Quark
- The constituents of nucleons, and the evidence for them.
- Radiation dose
- Absorbed, equivalent and effective dose, and why the units are not interchangeable.
- Radioactive decay
- The exponential law, the half-life, and activity as the only thing decay is actually used for.
- RIKEN
- The Japanese lab with the superheavy element discovery work and a strong open-data programme.
- Semi-empirical mass formula
- Nuclear mass and binding energy from a handful of fitted terms. The first model anyone writes and it still works.
- Serpent (Monte Carlo code)
- The open-source lattice physics code behind a large share of published reactor calculations.
- SL-1 accident
- The only fatal reactor accident in US history, caused almost entirely by a procedure.
- Small modular reactor
- Factory-built reactors. The current argument about nuclear power in the West.
- Standard Model
- Where the nuclear forces sit within the particle physics framework.
- Strong interaction
- The strongest force, and why it is confined rather than seen directly.
- Three Mile Island accident
- Slam shut, did not melt. The event that ended public confidence in nuclear power in the US.
- Tokamak
- The magnetic confinement concept that made controlled fusion plausible.
- Trinity (nuclear test)
- The first detonation, and the observation of the critical mass that opened the era.
- Tritium
- The radioactive hydrogen isotope, its 12-year half-life and its breeding requirements.
- TU Darmstadt — theoretical nuclear physics notes
- Chapter-by-chapter lecture notes on nuclear structure theory, the nucleon interaction and ab initio methods.
- Weak interaction
- The force behind beta decay, and the only one that violates parity.
- Weapons of mass destruction
- The category, and the non-proliferation regime built around it.
Particle physics
- ATLAS experiment
- The ATLAS general-purpose LHC detector. Free data, papers and explainers.
- CERN — Large Hadron Collider
- How the LHC works, with excellent diagrams and plain-language explanations.
- CERN Open Data
- Real collision data from the LHC, released free. Analyse ATLAS and CMS yourself.
- CMS experiment
- The CMS general-purpose LHC detector. Public data and documentation.
- DESY — DESY Hamburg
- German accelerator lab. Free research news and public material.
- Fermilab
- US particle physics and accelerator lab. Free science, education and open data.
- Geant4
- Free toolkit for simulating particle interactions and detector response.
- GWOSC — Gravitational Wave Open Science
- The official open archive of gravitational wave detections. Free downloads.
- HEPSoftware.org
- Open-source tools for HEP: ROOT, Geant4, C++ analysis frameworks. All free.
- IceCube Neutrino Observatory
- Neutrino astronomy at the South Pole. Free data, outreach and science.
- INSPIRE-HEP
- The essential particle physics database: papers, talks, citations. Free and definitive.
- LIGO Laboratory
- Gravitational wave observatory. Free data, science explainers and outreach.
- LIGO Open Science
- Release of real gravitational wave data for anyone to analyse. Free.
- Particle Physics 101
- A free, beautifully illustrated introduction to particles and forces. Best starting point.
- Physics Stack Exchange — particle physics
- Community Q&A on particle physics and the Standard Model.
- ROOT (CERN)
- The data analysis framework used by almost every particle physicist. Free.
- SLAC — Stanford Linear Accelerator
- Discovery lab for the quark and the positron. Free science and history.
- Snowmass
- US particle physics community planning. Free reports, great for learning the field.
- Standard Model overview (Symmetry)
- Free, clear guide to how the Standard Model fits together. Start here.
- Subatomic Cafe
- Free, friendly, well-written particle physics explainers. Highly recommended.
Quantum & Atomic
- Amazon Braket notebooks
- Free quantum computing notebooks you can run in the cloud.
- Atomic Archive
- Free history of atomic science with images and experiments. Good for intuition.
- CERN — antimatter and the LHC
- Free explainers on antimatter, dark matter and the LHC programme.
- CERN — particle physics explained
- Free particle physics explainers at every level, CERN official teaching material.
- CERN — the particle physics lab
- CERN's public site: science, education, open data. Free outreach material.
- Cirq documentation
- Google's free open-source quantum computing framework and its free tutorials.
- Einstein Online — explained physics dictionary
- Max Planck Institute free illustrated explainers of relativity, quantum theory and more.
- IAEA — nuclear science resources
- Free nuclear and radiological educational material, data and safeguards resources.
- IAEA Nuclear Data Portal
- Free evaluated nuclear data, decay data and live charts.
- IBM Quantum Learning
- Free courses and case studies for quantum computing with Qiskit.
- Nielsen & Chuang — quantum computing notes
- The free course built around the canonical quantum computing textbook.
- Nielsen's Quantum Computing notes
- Nielsen and Matuschak's free textbook on quantum computation, fully open.
- NIST — quantum information
- US standards body for quantum computing and sensing. Free resources.
- Nobel Prize — 2015 tunnelling
- Free write-ups on quantum tunnelling and topological phases.
- Nobel Prize — quantum dots 2023
- Free write-ups on quantum dots and synthetic atoms.
- Nobel Prize — Quantum Physics
- The 2022 Nobel in Physics on entanglement. Free popular explanations.
- Nuclear Regulatory Commission (NRC)
- Free US regulatory info, radiation basics and public documentation.
- OpenStax University Physics Vol 3
- Free textbook covering quantum, atomic physics, nuclear physics and particle physics.
- OpenStax University Physics Vol 3 — nuclear
- Free nuclear physics: radioactivity, fission, fusion, particle detection.
- Particle Data Group — reviews of modern physics
- Free introductory review chapter on particle physics. Excellent starting point.
- PDG — Particle Data Group
- The review of particle physics: masses, widths, lifetimes. Free, definitive.
- PennyLane documentation
- Free open-source quantum machine learning library from Xanadu. Great docs.
- Preskill — quantum information
- Free Caltech lecture notes on quantum information theory. The standard free text.
- ProjectQ — open-source quantum
- Free open-source quantum computing framework. Small, readable Python+C++.
- Qiskit (IBM) — open-source SDK
- The most widely used open-source quantum SDK. Free to install and learn.
- Quantum Country
- Free interactive essays that teach quantum computing and QM intuition. Outstanding.
- Quantum Mechanics — Stanford course
- Free Stanford undergraduate quantum mechanics materials.
- Stanford Encyclopedia of Philosophy
- Free peer-reviewed philosophy reference. A gold standard, check its index.
- The Atomic Heritage Foundation
- Free history of nuclear science and its cultural impact.
- US DOE — NNSA
- US nuclear security administration. Free technical and educational material.
Test, Measurement & PCB Design
PCB & EDA
- Electronics Stack Exchange — PCB design
- Browseable expert Q&A on layout, stackups, EMC and manufacturability.
- FCC RF exposure and compliance
- The official rules on RF exposure limits. Read it before running a high-power transmitter.
- Free routing and placement tools
- Open-source autorouter and specification-compliant router for KiCad, Altium and Eagle boards.
- Gerber file format specification
- The Ucamco free specification for Gerber, Excellon and ODB++ manufacturing data. The PCB industry standard.
- KiCad footprint and symbol libraries
- Official free libraries of verified footprints and symbols, plus a community package repository.
- KiCad forum and mailing list
- Active community support for schematic capture and layout, with detailed answers from experienced users.
- KiCad GitHub and source
- The full open-source codebase. Reading parts of it is a good way to understand EDA internals.
- LibrePCB
- A newer open-source EDA tool with a strong focus on version-controlled design files.
- LTspice — Analog Devices simulator
- Free SPICE simulator with an enormous library of vendor models. Exceptional for power and RF design.
- PCB stackup and impedance control
- A well-regarded PCB fabricator whose free guides explain stackups, impedance and design for manufacture.
- QUCS — open-source circuit simulator
- Free GUI SPICE/Qucsator simulator with good RF and microwave component support.
- Qucs-S — RF and microwave simulator
- Open-source simulator specifically aimed at RF and microwave circuit design.
Test & Measurement
- Darkside — electronics design videos
- Deep, practical electronics design courses and teardowns from an experienced engineer.
- Keithley — test and measurement
- Precision measurement instruments plus free learning material on low-level electrical measurement.
- Keysight (Agilent) application notes
- Extremely thorough free application library covering RF, signal integrity and measurement technique.
- Metrology and measurement uncertainty
- NIST's free technical guides on measurement accuracy. The authoritative reference.
- NanoVNA — pocket vector network analyser
- Open-source VNA firmware and hardware. Measures S11, return loss and antenna impedance for very little money.
- NIST calibration services guides
- Free guides covering the physics and practice of accurate instrument calibration.
- Rigol — oscilloscopes and instruments
- A major instrument maker whose manuals and application notes are freely available.
- Saleae Logic software
- Excellent free logic analyser software with a large library of protocol analysers. Works with cheap hardware.
- Siglent instrument resources
- Another instrument manufacturer with free manuals, firmware and application notes.
- SignalHound spectrum analysers
- Manufacturer of low-cost RF measurement instruments with free software and documentation.
- SMD component reference
- Identify surface-mount components by package markings. Essential for any modern board work.
- Soldering and rework resources
- A genuinely good free guide to soldering, desoldering and rework. Foundation skill for radio work.
Science
Research data
- Apache Arrow
- The columnar memory format that made zero-copy analytics practical across languages.
- Apache HBase
- The scalable random-access store. The design is hard but the paper explains why.
- Apache Hudi
- Incremental data processing on the lakehouse. The upsert story for streaming ingestion.
- Apache Iceberg
- A table format for huge analytic datasets. Hidden partitioning and schema evolution done properly.
- Binder — reproducible notebooks
- Turn any Jupyter repo into a working live notebook. Free and open.
- Copernicus Climate Data Store
- Free ERA5 and satellite climate reanalysis data. The standard.
- Data management plan
- Deciding up front what you will collect, keep and publish. Required by most funders.
- Data sharing principles
- How to publish data so others can actually reuse it. Underappreciated until a project ends.
- Data version control (overview)
- The underlying idea, and why applying it to data needs different primitives.
- DataCite
- DOI registration for datasets. The metadata standard most repositories implement.
- Delta Lake
- A different answer to the same problem, with a very readable design document.
- Dryad
- Curated, citable data publishing. Used by major journals.
- DVC
- Git-style versioning for datasets and model weights, the practical answer to ‘which data version produced this result’.
- EMB-EBI — bioinformatics
- The European Institute of Bioinformatics: ChEMBL, UniProt, PDBe, Expression Atlas.
- FAIR data principles
- Findable, Accessible, Interoperable, Reusable. The most adopted standard for research data.
- Figshare
- Free repository for figures, datasets and posters. DOI on deposit.
- Galaxy — web bioinformatics
- Free online platform for genomic analysis. No install, no cost.
- GWAS Catalog
- All published genome-wide association studies, free to browse and download.
- Harvard Dataverse
- Full-featured research data repository. Install your own too.
- Jupyter
- The notebook standard for exploratory work, and the file format behind most published analyses.
- Mendeley Data
- Free data storage with DOI publishing.
- Metadata
- Data about data. Without it a dataset is unusable, however interesting the rows.
- NASA Open Data
- Free satellite, climate and science datasets.
- NCBI Gene and Genome Data Viewer
- Free genomic datasets and tools from the NIH. Essential for biology.
- NOAA — National Centers for Environmental Information
- Free weather, climate and ocean data, plus the observational datasets.
- Open data
- Data that is free to use and reuse, and the licensing question behind it.
- OpenStreetMap
- The free, open map of the world. Fully open data.
- Parquet
- The on-disk columnar format almost everything in data engineering reads.
- Protein Data Bank (RCSB)
- The world's 3D structures of proteins and nucleic acids. Free and canonical.
- Reproducible research
- The crisis, and the practical standards that have emerged for fixing it.
Science
- Aeon — science essays
- Free long-form essays on science, philosophy and society.
- American Scientist
- Sigma Xi quarterly. Free, well-edited, covers everything.
- Atomic Scientists — nuclear glossary
- Free plain-language glossary of nuclear terms. Very useful.
- Bulletin of the Atomic Scientists
- Free magazine on nuclear weapons, climate and global security. Serious journalism.
- Center for Open Science
- Free resources and tools for reproducible research. Very practical.
- Data Management Plans — DMPonline
- Free tool and templates for writing data management plans. Required by many funders.
- Directory of Open Access Books
- Free searchable index of peer-reviewed open access books. Very useful.
- ESA — European Space Agency
- Space science explainers, mission data and images. All free.
- EurekAlert — press releases
- Free daily research press releases from labs worldwide. Discovery feed.
- EurekAlert!
- Free press releases from every university and lab on Earth. Excellent discovery feed.
- FAIR principles — GO FAIR
- Free explanation of the FAIR data principles. Short and clear.
- Federation of American Scientists
- Free analysis of science and technology policy. Very clear and rigorous.
- Institute for Health Metrics (IHME)
- Global Burden of Disease data and the GHDx tool. Free, downloadable.
- Internet Archive — science
- Free archive of books, journals and old software. An endless resource.
- Journal of Open Source Software
- Free, quick peer-reviewed papers describing research software. Very useful.
- Khan Academy — Science
- Free, excellent K-12 science: biology, chemistry, physics, anatomy.
- NASA Science
- NASA's public science site: astronomy, physics, earth and biosciences.
- National Academies of Sciences
- Free consensus reports on health, climate, space and more.
- National Academies Press (NAP)
- Thousands of free, downloadable expert reports. Register once, read everything.
- Nature — latest research
- Free selected articles and abstracts from the Nature portfolio.
- Nature — news
- Research news from the Nature editorial team. Some paywalled, plenty free.
- Nautilus — physics
- Free philosophy-of-physics essays. Genuinely changes how you think.
- Nobel Prize — official
- Every laureate, lecture and popular explanation. Free video and full text.
- Open Book Publishers
- Free open access scholarly books across science and social science.
- Open Science Framework
- Free platform for preprints, projects and data. The OSF mirrors many fields.
- OpenLearn (Open University)
- Free university courses and materials across science, health and social science.
- Our World in Data — health
- The best data visualizations on health, disease and life expectancy.
- Phys.org
- Phys.org and its sister sites (medicalxpress, techxplore) cover all the sciences.
- Project Gutenberg — science
- Free classic science texts: Darwin, Faraday, Maxwell, Hooke.
- PubPeer
- Post-publication peer review. Where image manipulation and bad stats get caught.
- Quanta — biology
- Free deep reporting on life sciences, from single cells to ecosystems.
- Quanta — computing
- Free deep reporting on computer science, algorithms and AI.
- Quanta — physics
- Free deep reporting on fundamental physics. Best in the world.
- Quanta Magazine
- The best science journalism there is. Free, rigorous, beautiful. Read weekly.
- Quanta Magazine — mathematics
- Free deep reporting on pure mathematics and the people behind it.
- Retraction Watch
- Which papers got retracted and why. Sobering and important.
- Scholarpedia
- A free, peer-reviewed encyclopedia written by scientists. Living, citable, trustworthy.
- Science advances
- Free selected articles from Science Advances, an open access journal.
- Science Magazine news
- AAAS flagship. Abstracts free, full articles often paywalled.
- Science Media Centre
- Free expert comment on hot scientific topics. Great for finding researchers fast.
- Science News
- Concise weekly roundup of research in every field. Very readable.
- ScienceDaily
- Daily research summaries across every field. High volume, filterable.
- Sense About Science
- How to read the science news without being fooled. Practical guide.
- Skeptical Inquirer / CSI
- Committee for Skeptical Inquiry. The reference for debunking bad science.
- Smithsonian — Science
- Research reporting with a public-science slant. Very readable.
- The Carpentries — open lessons
- Free, excellent open lessons on shell, Git, Python and R for research.
- The Carpentries — reproducible research training
- Free, practical training in reproducible scientific computing. Excellent.
- The Conversation — Science
- Academics explain their own work in plain language. Free, no paywall, no hype.
Science news
- Astronomy Picture of the Day
- A free, gorgeous astronomy image with explanation, every single day.
- CERN Courier
- Particle physics and cosmology news and features. Free.
- Chemistry Europe
- Chemistry research news across Europe. Free features.
- Chemistry World
- RSC's chemistry news and features. Free, well written.
- ESA — science & technology
- ESA mission news and results.
- Futurity
- Research news written for non-specialists. Very readable.
- Medical Xpress
- Health and medicine research news, from the Phys.org network.
- NASA breaking news
- Missions, discoveries and images straight from NASA.
- New Scientist — highlights
- Physics and science highlights. Headlines free, articles paywalled.
- Phys.org — latest
- All the physical sciences: physics, chemistry, astronomy, technology.
- Physics Today
- APS's magazine: research news, job advice, community. Some free.
- Physics World
- IOP's physics news. Broad, well-edited, much free.
- r/askscience
- Ask a scientist anything. Answers are usually rigorous and sourced.
- r/chemistry
- Chemistry research, industry news and lab life.
- r/EverythingScience
- Cross-disciplinary science posting, useful for breadth.
- r/physics
- Physics papers, questions and discussion.
- r/science
- Active community discussion of new papers. Insightful comments.
- Science in School
- Free teaching material for schools, aligned to curricula.
- Science Magazine — news index
- Top science news with expert quotes and context.
- SciShow
- Fast, accurate science news in video and podcast form. Free.
- SciTechDaily
- High volume research summaries. Useful keyword scanning.
- Symmetry magazine
- Particle physics stories from Fermilab and SLAC. Best popular particle writing.
- TechXplore
- Engineering and technology research news.
Learning & Pioneers
Self-taught learning
- Automate the Boring Stuff with Python (free)
- A free complete Python book for absolute beginners. Very practical.
- Clojure for the Brave and True (free)
- A free excellent Clojure book covering both basics and real practice.
- Dive into Python 3 (free)
- A free in-depth Python book. Good for understanding the why.
- Eloquent JavaScript (free book)
- A free, excellent JavaScript book that teaches the language properly.
- Haskell School of Expression (free)
- A free intro to Haskell as a functional language, with graphics.
- javascript.info (free)
- The free best-structured JavaScript tutorial on the web. Outstanding.
- Learn You Some Erlang for Great Good (free)
- A free fun introduction to Erlang and OTP. Very good for concurrency.
- MIT Rust course (free)
- A free MIT-style Rust course. Very practical and well structured.
- Problem Solving with Algorithms and Data Structures (free)
- A free Python textbook on algorithms and data structures. Excellent.
- Real World OCaml (free book)
- A free book on practical OCaml. Very well written.
- Think Python (free)
- Downey's free Python book that teaches computing as well as Python.
- You Don't Know JS (free)
- Free in-depth books on JavaScript mechanics. Deep and rigorous.
Tech pioneers
- Adam Back — hashcash (free)
- Free explanation of hashcash, the proof-of-work idea behind Bitcoin.
- Alan Kay's page
- The Dynabook and OOP visionary's free page and writings.
- Bret Victor — Worry Dream
- Bret Victor's writing on computing, tools and education. Highly original.
- Chuck Peddle — the 6502 story
- Free Commodore 64 and 6502 reverse engineering. Legendary resource.
- Dave Thomas (Pragmatic Programmer)
- The Pragmatic Programmer's site. Free articles on software craftsmanship.
- Douglas Hofstadter's site
- Gödel, Escher, Bach and Hofstadter's laws. Free writing on mind and computation.
- Eric Sink — Sink of the Border
- Free blog on version control, tools and developer productivity. Excellent.
- Ethereum whitepaper (free)
- The free primary source for Ethereum's design.
- Guy L. Steele's page
- Common Lisp and Scheme co-designer. Free papers, talks and writings.
- Hal Finney — reusable proof of work (free)
- Free early Bitcoin design documents. A fascinating primary source.
- Handmade Network (free)
- Free community of developers making games and tools from scratch. Great.
- Hans Boehm's blog
- Free writing on garbage collection, compilers and language design. Rigorous.
- Id Software open source (free)
- Free open source releases of classic game engines from John Carmack's studio.
- Inferno — Plan 9 virtual machine (free)
- Free docs for Inferno, the Plan 9 successor. Fascinating design.
- Jaron Lanier
- Free writing on virtual reality, digital rights and the future. Influential.
- Jef Raskin — Motherfucking Software
- Jef Raskin's free manifestos on software and design. Hilarious and profound.
- Joe Armstrong — Erlang
- The Erlang creator's free blog on concurrency and functional programming.
- John McCarthy's papers (free)
- The original AI papers and essays, free. A primary source.
- Michael Munday's blog
- Free blog on compilers, language design and research papers. Deep.
- Pavel Panchekha's blog
- Free blog on Go, Go internals, hardware and language design. Very strong.
- Philip Greenspun's blog
- Free essays on software, the web and startups from a veteran. Sharp.
- Plan 9 from Bell Labs (free)
- Free documentation and papers from Bell Labs' Plan 9 OS. Very deep.
- Raymond Chen — Old New Thing
- Free posts explaining Windows internals and how it all actually works.
- Retrocomputing Stack Exchange (free)
- Free Q&A on old hardware and software. Deep and friendly.
- Ron Jeffries' blog
- xUnit and Extreme Programming. Free writing on agile and TDD. Influential.
- Russ Cox's blog
- The Go creator's free blog on concurrency, C and systems. Essential.
- Sam Altman's blog
- Free writing on AI, startups and what comes next. Very well argued.
- Stallman's writings (free)
- Free writing from the founder of the free software movement. Provocative.
- Ted Nelson — Hypertext
- The inventor of hypertext on his own work. Primary source, free.
- The Bitcoin whitepaper (free)
- The free primary source. Nine pages that changed the world.
- The Digital Antiquarian (free essays)
- Free, beautifully written essays on the history of computer games.
- Tim Bray's Ongoing
- The co-inventor of XML on Java, HTTP and the web. Outstanding writer.
- Tim O'Reilly's Radar
- Free essays on software and technology trends from O'Reilly's founder.
- Turing's paper — computing machinery (free)
- The free primary source on computability. A landmark paper.
Site Reliability & Big-Tech Engineering
Site Reliability
- apenwarr — logs and outages
- Adam Wiggins on running small systems, with real outage write-ups and strong opinions about complexity.
- Aphyr's essays
- Aphyr's writing on distributed systems, network queues and outages. Rigorous and hard to forget.
- Ben Evans — on-call and operations
- Essays on the human and technical side of running software in production.
- Cloudflare blog
- Reliability, networking and systems engineering at global scale, with unusually honest post-mortems.
- Computer performance
- Latency and throughput as the two axes, and the queueing theory underneath them.
- Incident management
- The discipline of running incidents: roles, comms, and the postmortem culture that makes it better.
- Mean time to recovery
- MTTR, MTTD and why detection time usually dominates the real cost of an incident.
- Network congestion
- Why throughput collapses past a threshold. Useful mental model for any queue that backs up.
- Network throughput
- Goodput versus throughput, and why the two terms are not interchangeable.
- Observability
- The distinction from monitoring, and why cardinality is the thing that will hurt you.
- Raph Levien
- Writes about SQLite, bots and the craft of software, with a genuine engineering aesthetic.
- Redundancy (engineering)
- Where redundancy helps, where it just multiplies the ways to fail, and correlated failures.
- Runbook
- Written procedures for operations. The highest-leverage documentation in an on-call rotation.
- Service-level objective
- SLOs, SLIs and SLAs, and why targeting 100% guarantees outages.
- Site reliability engineering
- The discipline defined, and how it differs from traditional operations.
- Uber engineering
- Large-scale systems and the organisational reality of building them.
History, War & Conflict
World War I & II
- Adolf Hitler
- The biographical entry, which is the framing most specialist accounts reject in favour of structural explanation.
- Alan Turing
- At Bletchley and afterwards, and the biography of the man who made the method work.
- Army of the Soviet Union
- The Red Army's mobilisation and the eastern front, the decisive land campaign.
- Atomic Heritage Foundation
- The history of nuclear technology, including the Manhattan Project, with photographs and documents.
- Battle of Guadalcanal
- The first major Allied offensive, and the grinding attrition that preceded island hopping.
- Battle of Kursk
- The largest tank battle ever, and the end of German offensive capability on the eastern front.
- Battle of Midway
- Carrier combat and intelligence that broke the Japanese offensive capability.
- Battle of Moscow
- The first German strategic defeat, and the one that stopped the advance.
- Battle of the Atlantic
- The war of attrition that Britain actually fought, and the Ultra intelligence that won it.
- Benito Mussolini
- The Italian dictator and the founder of fascism.
- Berlin Wall
- The Cold War division of Europe, from 1961 to 1989.
- Bletchley Park
- The codebreaking station, the bombe, and the traffic analysis that made Ultra possible.
- Casualties of World War I
- The numbers, the sources behind them, and how much disagreement there still is.
- Casualties of World War II
- Military and civilian deaths, broken down by country, with the demographic consequences.
- D-Day
- 6 June 1944, and the deception and weather that made the landing possible.
- Eastern Front (World War I)
- The largest and least known part of the war, where most of the casualties were.
- Enigma machine
- The cipher, its design, and the long Polish and British effort to break it.
- Flamethrower
- First used in quantity in 1915, and the first genuinely modern weapon of the war.
- Franklin D. Roosevelt
- US president throughout, and the architect of Lend-Lease and the UN.
- Gallipoli campaign
- The failed 1915 campaign. Churchill's most serious political defeat and the model for a campaign going wrong.
- Hirohito
- Emperor through the war, including the decision that was not to surrender.
- Hiroshima
- The bombings, the orders, the estimates and their revisions. The most argued-about event in the war.
- Historiography of World War II
- How the war has been written, and where historians disagree. The most valuable thing to read after the facts.
- Holocaust
- The genocide itself, and the historiography of how it happened.
- Imperial Japanese Navy
- The naval arm that did not decline as expected, which is why Midway mattered so much.
- Imperial War Museums
- The UK's war museums, with a first-class archive of photographs, films and documents.
- IWM collections
- Searchable catalogue of IWM holdings, most of them digitised and freely downloadable.
- Joseph Stalin
- Soviet leader, and the tension between alliance and suspicion that shaped the eastern campaign.
- Jutland
- The only major naval clash between the British and German fleets, and still arguable who won.
- Khan Academy — World History 1
- Free courses with video and written materials, covering both wars and their backgrounds.
- Khan Academy — World History 2
- The second half, including the world wars and the Cold War in detail.
- League of Nations
- The failed collective security experiment, and the blueprint for the UN.
- Luftwaffe
- The German air force across both world wars, and the Battle of Britain.
- Nagasaki
- The city and the second bombing, and the different yield that made it the actual choice.
- National WWII Museum — research
- The museum's dedicated war-history pages, useful as an overview with curated sources.
- Nazi Germany
- The state itself: how it was built, run and collapsed.
- Nazi Party
- From a small party to a total state, with the internal dynamics that made it work.
- Normandy landings
- The landings themselves, and the Mulberry harbours that solved the logistics problem.
- NPS — World War II
- US National Park Service interpretation of the war, from Pearl Harbor to the surrender.
- Nuremberg trials
- The trial, the categories of crime, and the principle of individual criminal responsibility.
- OER Commons
- Aggregates open-licensed history teaching material you can reuse freely.
- Operation Barbarossa
- The largest invasion in history, and the campaign that destroyed the German army in the east.
- Operation Husky
- The invasion of Sicily. Churchill called it a dress rehearsal; he was more right than he knew.
- Operation Overlord
- The wider operation around the landings, including the air campaign before it.
- Royal Navy
- The second largest navy in the world for most of the war, and the convoy work that mattered most.
- Sinking of the Bismarck
- Hunting down one ship in 1941, and what it cost to do it.
- Somme
- The first day of the Somme and the 1916 offensive. The clearest illustration of industrial attrition.
- Spartacus Educational
- Straightforward summaries of campaigns, weapons and equipment. Useful for orientation, not for depth.
- Standard Ebooks
- Carefully proofread public-domain texts, many of them the canonical war memoirs.
- The American Legion
- US veterans organisation, with a substantial military research library.
- The National Archives (UK)
- The primary British record, including the War Cabinet papers and Admiralty files.
- The National Archives (US)
- The US record, with the Franklin D. Roosevelt library and the captured German records.
- The National WWII Museum
- New Orleans based, with excellent research collections and oral histories.
- Third Reich
- The regime's structure and the distinction between Nazi Party and German state.
- Treaty of Versailles
- The full text, the terms, and the argument about whether it caused the Second World War.
- Trench foot
- A disease of static warfare and what the static conditions did to the men in them.
- United States Navy
- Rapid wartime expansion, and the carrier and submarine campaigns.
- UNT Digital Library
- An enormous collection of historical photographs and documents, largely public domain.
- USHMM Holocaust Encyclopedia
- The most reliable free reference on the Holocaust, with a substantial document archive.
- Verdun
- The longest battle of the war, and the attrition that consumed both sides.
- Warsaw Uprising
- Sixty-three days against the Wehrmacht, and what it cost the city and the Poles.
- Wehrmacht
- The German armed forces, and the distinction between the army and the SS that matters so much.
- Western Front (World War I)
- Four years of essentially static attrition, and why it stayed static.
- Wikisource
- Primary documents: treaties, speeches, diaries, official reports, in translation and in the original.
- Winston Churchill
- British prime minister through the whole war, and the war leader role in practice.
- World War I
- The whole conflict, with causes, course and consequences in one place.
- World War II
- The same, and the most consequential conflict in recorded history.
- Yad Vashem
- The Israeli national memorial. Names, testimony and family material, largely searchable.