Xonotic is a free and open-source first-person shooter video game. It was developed as a fork of Nexuiz, following controversy surrounding the game's development. The game runs on a heavily modified version of the Quake engine known as the DarkPlaces engine. Its gameplay is inspired by Unreal Tournament and Quake, but with various unique elements.

Nexuiz is a free first-person shooter video game developed and published by Alientrap. The game was released under the GNU General Public License (GPL) and uses the DarkPlaces engine, a modified Quake engine. A remake, also called Nexuiz, was released for Steam and Xbox 360 using CryEngine 3. The original game was released on May 31, 2005.