Open Quartz is a GPL game with GPL content based on the Quake engine. The gameplay of Open Quartz is very similar to Quake, but the single player game is limited to fighting monsters and bots in deathmatch levels. Open Quartz uses minimally modified GPL Quake C code and replaces every graphic and sound effect with an identically named file, so it is compatible with many Quake mods. * Homepage: * Sourceforge project: