A preview of Xonotic 0.1--a free, open source, licensed under GPL, first person shooter game--is now available.
Xonotic 0.1 is a fork of the the Nexuiz (2.5.2) game and according to the developers, Xonotic continues where Nexuix ended.
This first preview, which is available for download, has a limited number of maps, with new maps being worked on for future releases.
More information, screenshots, demo videos, and more and can be found on the Xonotic website.