Nexuiz is based on the Darkplaces engine. The darkplaces engine is an advanced Quake1 engine developed mainly by Forest "LordHavoc" Hale, who has been working with the Quake1 engine for many years.
A few of Darkplaces main features are Quake3bsp support, realtime lighting and shadowing, new particle effects, advanced menu system, and Md3/Md2 model support. Because Nexuiz is based on the Quake1 engine, its source code along with its content is entirely GPL.
Nexuiz focuses on bringing the FPS back to the basics with quick, lethal battles and balanced weaponry. As of the current release there are 9 weapons and 24 official maps, as well as 15 player models, with an average of 2 skins each.
Nexuiz is primarily multiplayer (though it includes a full single-player campaign, which allows one to play through the various multiplayer game types and maps with bots), and allows for hosting and joining of games. It can also support new gametypes, or whole conversions quickly applied to it (much like Quake). Nexuiz supports most, if not all, Quake modifications (although with varying functionality). Currently there are a few custom mods and maps used.