Tremulous - Free Fast Paced Shooter Game for Aliens

Tremulous is a fast paced FPS (first person shooter) game. However, the gameplay is unlike most other FPS games because not only do you get to pick whether you want to be a human or an alien, but there are also other customizations allowed. If you are a human, you can upgrade your armor, improving both your looks and your battle skills. If you are an alien, you can upgrade your body, starting out as a small innocent looking spider, and later becoming a huge 10-foot tall and 8-legged horror. For more information see here. Detailed installation instructions for Ubuntu users can be found here.