Games On Net reports Alien Arena 2009 has been released, this is a free open-source shooter for Windows and Linux. You can download the game at Gamershell.
This time around, the game's been almost totally overhauled, with a "staggering" amount of improvements to the game engine. Full implementation of GLSL per-pixel lighting on all services sees the game come alive, especially when coupled with the OpenAL audio system and some spiffy new gameplay features. Optimisation has been a major focus, with the developers claiming that "No longer does one have to be leary of cranking the settings up, the game plays remarkably faster with the switch to GLSL for per-pixel operations."
Described as a "lean, clean fragging machine", the devs have made the statement that "This isn't your daddy's Alien Arena" - and it's a good few notches above last years model, boasting new and improved maps, music and sound effects.