Cool Links!

Web development

Nu Html Checker – validate an HTML document
W3C CSS Validation Service – validate CSS code or an HTML/XHTML document that contains CSS
WHATWG character entity reference chart – a list of named HTML character references like &
Official Unicode Online Data – a list of all Unicode characters as a single PDF (look for CodeCharts.pdf under a version directory)
Collection of 88×31 buttons
The 88×31 Archive – more buttons
The Largest 88×31 Collection on the Internet – more buttons
A.N. Lucas's 88×31 button Collection
88×31 Collection
buttons world – a small collection of 88×31-px buttons
Indigo's den – Links (88x31 and more!) (xaselgio.net)

Programming and game hacking

Bit Twiddling Hacks – algorithms/C snippets regarding mathematical/bit operations (e.g. determine if an integer is a power of two)
The Daily WTF – software development humor
Data Crystal – technical info about games (e.g. lists of ROM/RAM addresses)
ModdingWiki – technical info about games (e.g. file formats)
Near's Respite (mirror 1, mirror 2) – game console emulators, development tools, articles about emulation (RIP Near)
NESDev Wiki – technical info about the Nintendo Entertainment System
NESDev Forum – more of the same
Programming the 65816 - Including the 6502, 65C02, and 65802 – a PDF book
ROMhacking.net – files regarding game hacking (e.g. documents, utilities and ROM patches)
The ryg blog – programming
Home Page of Evan Miller – math and programming articles (e.g. Splatoon's ranking system)
Game Boy development resources
Int10h – VileR's blog – retro PC stuff
The blog at the bottom of the sea (demofox.org) – programming
lisyarus blog – game development

Games

The Cutting Room Floor (TCRF) – hidden content in games (e.g. debug menus and unused graphics)
Doom Wiki – detailed info about the Doom game series
KeenWiki – detailed info about the Commander Keen game series
MobyGames – a lot of non-technical info about games
Nerdly Pleasures – in-depth blog posts about retro gaming
TASVideos – tool-assisted speedruns of (mostly old) games
DOS haven – modern DOS games
NESWorld – retro gaming (NES homebrew etc.)
NESCartDB – technical info about NES game cartridges

Misc computer stuff

Dhole Moments (Soatok's blog) – cryptography, furries
deneb (leggi.es) – OS images etc.
moule world – links – including 88×31-pixel buttons
Absorptions (windytan.com) – O. Räisänen's blog; signal processing
Byte Cellar – retrocomputers
eevee's Fuzzy Notepad – game development, furries, etc.
Hackaday – hardware hacks every day
homepage of Gravis – old computers
Hugo Landau – computer articles
Joel Yliluoma (Bisqwit)'s home page
Ken Shirriff's blog (righto.com) – CPU die shots etc.
Reenigne blog – “8086 microcode disassembled” etc.
Nicole Express – a retro gaming hardware blog
ToughDev – vintage computing – retro PC articles
Software Folklore – interesting computer bugs
The Cursed Computer Iceberg Meme – interesting computer bugs
The Future Is Now – Misty's blog
ePanorama – hobbyist electronics
Vintage Computing and Gaming – Benj Edwards' blog
Vogons – a retro PC forum
MCbx Old Computer Collection (oldcomputer.info) – old computer stuff
GUIdebook – screenshots of operating systems
Ethically sourced Lena picture – a replacement for the well-known Lena/Lenna test image
ubitux/blog – programming, math
Lospec palette list – colour palettes for pixel art
programming pages (sirrida.de) – bit permutations etc.
Datagubbe – essays on computers, etc.
oldskool.org – retro PC stuff
thefox – NES development
Retro Game Mechanics Explained – articles (website of the Youtube channel)
chjara's links (archived)
Tom Forsyth's Tech Blog – some advanced stuff
Vogons – a retro gaming forum
David Buchanan's blog – advanced computer stuff (“SIMD in pure Python” etc.)
Just a QR Code – a QR code generator with no ads

(Spoken) languages

Language Log – a linguistics blog
Mark Rosenfelder's Metaverse – constructed languages, worlds and linguistics

Webcomics

Savestate – retro games and furries
Freefall – science fiction adventures of an alien and a wolf
General Protection Fault – working with computers (I haven't read very far yet)
StupidFox – a feral fox and his friends
VG Cats – cat characters playing video games
Runaway to the Stars – life in space

Misc

Wiby – a “search engine for the classic web”
Odoben's Corner of Space-Time – furry art, a guide to Mastodon
TuxedoDragon's Shapeshifter Shenanigans
Jae's home page – has a blog
The World of Sonic2k
NeoCities – free static web hosting
NekoWeb – free static web hosting (I haven't tried this one myself)
Atapi's Domain!
Lira's home page – Famicom keyboard etc.
Site Reliability Enby
FoxiMax – a Wordle-like game
Futility Closet – trivia blog posts (history, math, etc.)
The On-Line Encyclopedia of Integer Sequences – what's the sequence that starts with 1,1,2,3,5,8,13,21,34,55 called?
Semantle – a Wordle-like game based on semantics
Guess My RGB – try to estimate the amounts of red, green and blue in the color shown
Wikimedia Downloads – offline copies of Wikipedia in XML format
Annies blog – scifi, tech, geekery
Azimuth – a science blog
Kamuniak's furry photo gallery – EuroFurence, NordicFuzzCon, etc.
A List Of Games By Trans People Before 2010
InterACT – resources for intersex people and their allies
Erich Friedman – packing of geometric shapes etc.
Col. Sicherman's Home Page – geometry etc. (archived)
Booting Linux on Intel 4004
GUIdebook – screenshots of graphical user interfaces
OldVersion – old versions of programs
Zen of Assembly Language: Volume I, Knowledge – a book by Michael Abrash
CPU Collection – photos of CPUs
Morsle – practise listening to Morse
Scary Beast Security – Chris Evans' blog
jsgroth’s blog – emulator development
Wplace – draw on a map of the world
The Universe of Discourse – Mark Dominus' blog
oldskooler ramblings – Trixter's blog
Collection of series for pi
DiscMaster – search old files from Internet Archive
The 7 segment decoder, done wrong – uses modified BCD
Train Planner – a small online strategy game by Toffee