Xonotic (/zoʊˈnɒtɪk, ksoʊ-/) 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 similar to the Quake 3 Arena series of games, but with various unique elements.

There are sixteen different game modes in Xonotic, including classic modes like deathmatch and capture the flag. In order to unlock more game modes, players must complete different levels of gameplay. To score points, players must kill enemies using futuristic weapons while completing objectives. The gameplay is very fast-paced, due to players being able to move at high speed and jump erratically. While the basic concept is inspired by other games of the same genre, there are several unique elements. Emphasis is placed on movement and player physics, with a focus on gaining speed, jumping great distances, and conquering the level geometry. This is done with classic techniques including strafe jumping, bunny hopping, and rocket jumping. Weapons have special abilities such as multiple fire modes, which increase the tactical options available to the players.

The game features a futuristic aesthetic, with maps set in high-tech environments and in space. The game runs on the DarkPlaces engine and thus supports bloom, dynamic lighting and shadowing, offset mapping, and high-dynamic-range rendering. The developers claim that the graphics quality is comparable to commercial video game titles released between 2006 and 2007.

Players can also personalize their HUD according to their exact preferences.

In March 2010, controversy arose over the original Nexuiz being licensed to IllFonic to create a commercial version. The original creator, Lee Vermeulen, secretly made a deal with IllFonic which gave them hold over the Nexuiz trademark. Since this turn of events was unexpected by the community and most Nexuiz developers, they promised to create a fork controlled by a community in an open manner. Approximately seven months later the source code was published via Git. A preview version was released on 23 December 2010.

Version 0.5 was released on 8 September 2011. It featured multi-language support, seven new maps, vehicle support, and enhancements to weapons and player movement, among other changes. Since the release of this version, Team Xonotic's stated aim has been to "create the best possible fast-paced open-source FPS game".

Version 0.6 was released on 8 March 2012. It added sRGB lightmap rendering, a new menu interface, 4 new maps, an integrated statistics system (XonStats), a Sandbox editing mode and the long-awaited feature of ClientSide QuakeC (CSQC) networked players. Bug fixes and optimizations were also made.

Version 0.7, was released on 8 June 2013. It featured client-side rendering of players, 4 new maps and a complete re-write of the in-game chat system. Additionally, the team migrated to the gmqcc QuakeC compiler which generated faster, more optimized program files.