The flexible game engine
The ioquake3 community effort to continue supporting/developing id's
Orx: Portable Game Engine
0 A.D. is a free, open-source, cross-platform real-time strategy game.
A free 3d game for PC that does not limit the player. Fight,Build,Gain
A cross-platform port of Hexen II game.
Updated emulator of Forgotten Realms: Unlimited Adventures
A cross-platform, open-source, pure C game engine for mobile game
Retro game engine for creating games like it's 1997
Based on the raedwulf-et project
A Marathon (first-person shooter) engine with enhanced features
Game engine for playing tomb raider 1 - 5 levels.
DarkForest, the Facebook Go engine
The IRC's Talking Robot
A Simple Game Engine
Tactical, turn-based game engine, that uses OpenGL and WinAPI
Yet Another Chess ENgine
realistic truck & car simulator, with OpenGL graphics
Quake III Arena GPL Source Release