Real Time Strategy game engine supporting early Westwood classics
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
Spring is a free RTS engine developed for Windows, Linux and Mac OS X.
A cross platform Lua based game engine
An online multiplayer turn based strategy game and board game engine.