Multi Theft Auto is a game engine
Open-source engine for Heroes of Might and Magic III
fheroes2 is a recreation of Heroes of Might and Magic II game engine
Open source clone of the Age of Empires II engine
Real Time Strategy game engine supporting early Westwood classics
Voxel game-creation platform with easy modding and game creation
dhewm 3 main repository
The ioquake3 community effort to continue supporting/developing id's
RPG Maker 2000/2003 and EasyRPG games interpreter
Recreation of the classic Grand Theft Auto III game executable
An OpenGL RTS game engine written in C
Descent 3 by Outrage Entertainment
3D Procedural Game Engine Using OpenGL
A modern, cross-platform Quake game engine based on FitzQuake.
GemRB is a portable open-source implementation of the Infinity Engine
Game engine supporting many 3D/2D formats and graphic effects
A cell-based puzzle game featuring classic and completely new puzzles
PyCAPGE - Python Classic Adventure Point and Click Game Engine
A conservative source port of Hexen that is identical to DOS
A conservative source port of Heretic that is identical to DOS
A Tile-based Game Engine written in C# mimicing retro consoles.