Games
Actual games
Jstris
Online multiplayer tetromino game.
TETR.IO
Like Jstris, but pretty.
1000mines
Infinite Minesweeper game.
VIP Games
Free card and board games to play with friends online.
Hot Death Uno
Funny, dumb and sadistic Uno variant.
TitleRun
A game that's played in the title bar.
NationStates
A web-based nation simulation game.
EasyRPG
A free and open source reimplementation of RPG Maker 2000/2003.
Panel Attack
A very accurate, free, open-source, online multiplayer Panel de Pon / Tetris Attack clone.
Minetest
An open source voxel game engine. If you like Minecraft, this is for you.
Play Melty Blood!
The poverty fighting game by excellence. Download the community edition and have fun.
General
The Cutting Room Floor
A wiki dedicated to unearthing and researching unused and cut content from video games.
shmuplations
A repository of Japanese game development-related translations covering primarily arcade and console games from the 80s-90s.
Emulation General Wiki
A wiki dedicated to all things related to video game emulation.
/v/'s Recommended Games Wiki
A wiki dedicated to showcasing the best games on every system and featuring miscellaneous lists and guides.
Hard Drop
A wiki dedicated to Tetris.
Sonic Retro
The Sonic the Hedgehog resource second only to Sega.
Lemma Soft Forums
A forum dedicated to the discussion and creation of visual novels, with a focus on the Ren'Py software. Very active.
vgperson's Stuff
The site of one of the most prolific translators of Japanese indie games. She's done more than just games, so don't miss it!
It Runs Doom!
A blog dedicated to showcasing Doom running everywhere.
How Flash games shaped the video game industry
An article celebrating the influence of Flash on gaming, with retrospective comments by the creators of Flash and the people whose lives were changed by it.
Worms Knowledge Base
A wiki dedicated to the Worms games, specifically the classic 2D entries. Full of technical info.
ScaleyFoxy's Sonic Fan Game Archive
A site dedicated to the archival of late 90s to early 2000s Sonic fan games. Pretty odd design.
PSO2 Skill Simulator
A tool for planning the development of your PSO2 character. Game's dead though.
Bad Time Simulator (Sans Fight)
The final boss of Undertale in your browser.
Monkey Island Inflation
Never pay more than 20 bucks for a computer game, but adjusted for inflation.
Umineko screenshot generator
Make Beatrice insult Battler in any way you could imagine. It's like magic!
YoYo Games Archive
A searchable archive of the YoYo Games Sandbox, a portal that allowed people to upload and play Game Maker games that existed from 2007 to 2014.
SCUM Games
Games for TempleOS.
Attorney Online
A chat program based on Ace Attorney. An absolute blast.
Riichi Mahjong
Japanese Mahjong Wiki
A wiki dedicated to Japanese Mahjong.
Autotable
An online Riichi Mahjong simulator. The computer does not enforce the rules or make any moves for you.
Mahjongle / Alternative
Wordle with mahjong tiles.
Riichi Scoring Trainer 1 / Trainer 2
Train your ability to calculate han, fu and scores for riichi mahjong hands. The first one has a handy scoring reference and lets you type in your guesses, but the only feedback it offers is whether you got a score right or wrong, and how many. The second one does show a fu breakdown and lists the yaku in a hand, but it's not interactive (you can only reveal the answer) and doesn't have a reference.
Touhou Project
Touhou Wiki
A wiki dedicated to the Touhou Project.
Moriya Shrine
A site for all sorts of downloads related to Touhou, official and fan-made.
Touhou Patch Center
A community effort to translate all Touhou games. Home of the THCRAP, a tool that patches the games with community-provided translations as they run so prepatched binaries are no longer necessary.
Maribel Hearn's Touhou Portal
A big collection of resources for the Touhou community.
Easy Modo
Ehhh, really?
inaba.reisen
A handy Touhou site.
Walfas
Home of create.swf and many other classic Touhou flash animations.
Yume Nikki
YumeWiki
A wiki dedicated to Yume Nikki and its fangames.
Yume Nikki and Fangames Online
Play Yume Nikki, 2kki, .flow, and other fangames online with others. Use an adblocker to hide the onscreen controls. Server and client code is free.
Yume Nikki Online Project
Same thing, but with fewer games.
Uboachan
An imageboard dedicated to Yume Nikki.
Yumebooru
A booru-style imageboard dedicated to Yume Nikki illustrations.
Madotsuki's Closet
Another Yume Nikki fansite.
Yume Nikki Fan Game Archive
A repository dedicated to the backup of most if not all Yume Nikki fan games.
LaInvestigaciónYN
The homepage of the group of the same name dedicated to finding KIKIYAMA's lost works. They've successfully found and publicly archived versions 0.04, 0.06, 0.07, 0.08 and 0.09 of Yume Nikki.
Puyo Puyo
Puyo Nexus
A site dedicated to Puyo Puyo. The wiki contains a lot of info about the games and related material, and the recently closed forums hold some downloadable treasures that you'll have to find.
Puyo Puyo VS
An online multiplayer Puyo Puyo clone. Now free and open source!
The Puyo Puyo Library
A gallery of scans of Puyo Puyo manuals and covers. There's also an article about Puyo Puyo Box.
Hardcore Gaming 101's Puyo Puyo articles / Alternative
An excellent series of 11 articles telling the long history of the series, all the way from its birth to its 20th anniversary game.
Puyo Puyo Preservation Place
A blog dedicated to the archival of promotional material, assets, and other miscellaneous Puyo Puyo stuff.
Suzuran Library
An archive of rare Puyo Puyo / Madou Monogatari games.
Precise Museum
A Puyo Puyo fan translation group.