A modern, cross-platform Quake game engine based on FitzQuake.
Odamex is a free, cross-platform, modern client-server Doom engine
A cross-platform port of Hexen II game.
Hardcore 3D space shooter with spaceship upgrade possibilities.
GemRB is a portable open-source implementation of the Infinity Engine
WW2 U-boat simulation
functions for 2D/3D graphics + realistic driving simulation
Cross-platform real-time strategy game (3D)
Free MMORPG
3D-Accelerated open-source DOOM engine
3D driving simulation based on Open Dynamics Engine
a very lightweight advanced terrain-rendering and 3D map rendering sys
extreme 3D flight simulator with advanced terrain rendering
A cross-platform, 3D interpreter to play LucasArts' Lua-based games
Articulated-body simulation engine written in C