Technology and Programming

*NIX

Oh Shit, Git!?! (External)
Cool, but obscure unix tools (External)
Tmux Cheat Sheet (External)
Beautifully typeset and easily browsable man pages (External)
Command-line Interface Guidelines (External)

Assembly

Online x86 emulator (External)
WikiTI - Z80 Programming (External)
MarkeyJester's Motorla 68000 Beginner's Tutorial (External)

C/C

Wandbox - Online C/C compiler (External)
Pre-defined C/C compiler macros (External)
Simple Dynamic Strings library (External)
Tips for Optimizing C/C Code (External)
libdill: Strucuted Concurrency for C (External)

Platform: Nintendo Game Boy

GBDev (External)
Pan Docs (External)
GB Homebrew Hub (External)
GBZ80 Opcode Map (External)
WikiTI - Z80 Programming (External)
CatSkull - How to make Gameboy Chipmusic (External)
Official Game Boy Programming Manual v1.1 (External)
Emulating a GameBoy Cartridge with an STM32F4 (External)

Platform: Sega Mega Drive/Genesis

Aggregating Community Research (forum post) (External)
MarkeyJester's Motorla 68000 Beginner's Tutorial (External)
Mega Drive Development Wiki (External)

Platform: Sega Saturn

Archived official Sega Saturn documentation and tools (External)
RetroReversing - Saturn (External)
Yabause Wiki (External)
Sega Xtreme - SatDev (External)
Jo Engine (External)
InvisibleUp - Sega Saturn Notes (External)
The Rockin'-B's Saturn Game Tutorial and Demo (External)
Cyber Warrior X - Saturn Utilities (External)
List of untranslated Sega Saturn games (External)

Topic: Compression

NES Dev Wiki - Tile Compression (External)
Harder, Better, Faster, Stronger - Compression (External)

Reverse Engineering

How to Hack an Expensive Camera and Not Get Killed by Your Wife (External)
VB Sacred Tech Scroll - Virtual Boy Specifications (External)
Mainframe Hacking CYOA (External)

Game Development

Higher-Order Fun (External)
OpenGameArt.org (External)
Managore - m5x7 (font) (External)
Lazy Foo - Beginning Game Programming w/ SDL (External)
Generating Worlds with Wave Function Collapse (External)
The Textbook of Video Game Logic, Vol. 1 (pdf, large) (External)
Game Engine Black Books (DOOM, Wolfenstein 3D) (External)

Hardware Design

Analog Oscilloscope Pong (External)

Web Development

Font City hosted webfonts (External)
Fork Awesome symbol webfonts (External)
Easing Functions Cheat Sheet (External)
Chart.js charting library (External)

Gopher/Gemini

Mariteaux's Gopher Information Repository (External)
Gemini Project Homepage (External)

Health and Ergonomics

darebee - Hand stretches (Comic) (External)
Jordan Maeve - Ulnar nerve/"Funny bone" care (Tweet thread) (External)
Rama el Ligre - Hand stretches (Comic) (External)

Misc

Online LaTeX math editor/previewer (External)
Rust container cheat sheet (External)
Writing system software: code comments (External)
Professional Programmer's Guide to Fortan77 (External)
LunarLambda - A Best Effort Guide to Vim's Indentation Settings (External)