Multi Theft Auto is a game engine
fheroes2 is a recreation of Heroes of Might and Magic II game engine
Open-source engine for Heroes of Might and Magic III
Open source clone of the Age of Empires II engine
Voxel game-creation platform with easy modding and game creation
dhewm 3 main repository
RPG Maker 2000/2003 and EasyRPG games interpreter
Recreation of the classic Grand Theft Auto III game executable
Descent 3 by Outrage Entertainment
3D Procedural Game Engine Using OpenGL
GemRB is a portable open-source implementation of the Infinity Engine
RTSish Game Engine
An isometric arcade-style game of skill, puzzles and exploration
ZDoom 2.8.1 fork focusing on modernisation, performance and stability
C++ lightweight cross-platform game engine
A fork of dhewm3 with an emphasis on modernisation and vanilla Doom 3
Opensource crossplatform Fallout 2 game engine writen in C++ and SDL
a UCI chess engine
Spring is a free RTS engine developed for Windows, Linux and Mac OS X.
DOOM / Heretic / Hexen source port with enhanced graphics and UI
KlayGE is a cross-platform open source game engine