High Quality Content by WIKIPEDIA articles! Xonotic is a first-person shooter video game. It is cross-platform, free and open source software. It is a fork of Nexuiz, and is based on the DarkPlaces engine, a heavily modified version of the Quake engine. Gameplay is inspired by Unreal Tournament and Quake, but with various unique elements. Xonotic aims to become the best possible open-source FPS (first-person-shooter) of its kind.