All of Nexuiz is licensed under the GPL, including the core engine, the textures, maps, sounds, and models. It is extremely modder friendly. Because of its GPL license status, it can be included in any Linux distros or packages and is entirely free.
Nexuiz is built on the power of the Darkplaces engine, which is a heavily modified version of the original Quake. Darkplaces features realtime lighting and stencil shadows, bumpmapping, gloss, bloom, and totally rewritten network code that supports up to 64 players on a single server. While quality gameplay was our primary goal, it’s graphics technology and artwork allows the game to compete with the current quality of commercial games.
Any online deathmatch fan will instantly feel at home with Nexuiz’ weapons and movement style. The fast server browser and quick loading time allows you to jump right into a game at a moments notice and play a quick game. Available now at Nexuiz.com”
Link: nexuiz.com