YellowAfterlife

Sample project for Steam-based networking for GameMaker.
Convert DnD blocks in GMS1 projects to equivalent GML
Standard-issue compression/decompression functions for GameMaker games.
Dynamic scripting on Win/Mac/Linux.
A highly configurable loading screen extension for GMS' web games
Check/disable/dispatch window commands in GameMaker
Allows to convert BMFont format' bitmap fonts for use in GameMaker projects.

Multiplayer games/mods/collabs

An online multiplayer mod for Nuclear Throne.
GIF
A multiplayer NES'ish platformer
Platformer
GIF
Color Ninjas is a versus game that is all about randomness, power ups, cowardice and shouting at each other!
Action
2 Player (online+local) snake game with chickens and stuff
Sports
An online multiplayer mod for Wasteland Kings
Action
An online multiplayer mod for Super Crate Box
Action
A Spelunky Classic mod with online multiplayer.
Platformer
A 2-player card game with online multiplayer.
Strategy

Singleplayer games & collabs

GIF
A short minimalistic platformer game.
Platformer
Play in browser

Assets and examples

Convert DnD blocks in GMS1 projects to equivalent GML
Play in browser
Standard-issue compression/decompression functions for GameMaker games.
A highly configurable loading screen extension for GMS' web games
Check/disable/dispatch window commands in GameMaker
Allows to convert BMFont format' bitmap fonts for use in GameMaker projects.
GameMaker & Construct 2 plugins to let user to let user pick where to save screenshots.
Work with files in all accessible places in GameMaker games.
Brings back synchronous drawing into GameMaker: Studio.
Show progress bar in taskbar in GameMaker games
Window flashing/highlight/notifications for GameMaker
Better INI functions for GameMaker: Studio
Simple isometric example for GameMaker: Studio
Unified API for mouselock on desktop and HTML5 for GameMaker.

Userscripts & userstyles

Various usability tweaks for shoutbox on http://forum.hellroom.ru/
A userscript that displays repository descriptions when browsing Bitbucket.
Adds syntax highlighting for code posted on GameMaker forum.
GML snippet syntax highlighter for the GameMaker-centric subreddit.
GIF
A userscript for better image viewing experience in browsers.
A customizable userstyle for TweetDeck.
Play in browser
GIF
A userscript for compacting TweetDeck content to a usable state.
[ru] A userscript expanding on audio playback on VK (social network)
A userscript for viewing deleted messages on VK social network