Odamex is a free, cross-platform, modern client-server Doom engine
LGSL (Live Game for PHP 5.4-8+: online status for various gameservers
Utilities to make running a Linux Alien Arena server easier
Classic America's Army
DOOM / Heretic / Hexen source port with enhanced graphics and UI
Custom exp./level caps + autounlock engrams on ARK: Survival Evolved!
Web based Game server control panel
Quake C mods and support - SSQC / CSQC
Battlefield bad company 2 Master server emulator + Server R34
The famous Maze War game recreated as a modern web application.
MvMTrainer plugin provides 'training' mode for MvM matches of TF2
Cross platform administration tool for Source Engine dedicated servers
GraphOX is awesome
Cube2:Sauerbraten Mod with various features
A multiplayer First-Person-Shooter game built in Java 3D
Windows rcon GUI for CS:Source servers
A Co-op/Deathmatch Mod for half-life 2