Popular Linux game Nexuiz was forked into a new game Xonotic earlier this year as there was some disagreement between Nexuiz developers and community. Now Xonotic developers have released first preview version playable on Linux, Windows and Mac.
Xonotic is a free (GPL), fast-paced first-person shooter that works on Microsoft Windows, Mac OSX and Linux. Xonotic is a direct successor of the Nexuiz Project with an aim to improve and redo game code, graphics etc. A look at how Xonotic will be different from Nexuiz:
* A more unified and consistent art direction
* New player models and animations
* New set of default maps, some of them will get a makeover
* New sounds and music
* New stronger bot AI
more here  w/ screenshots