ok, so an interesting title for a game. Whats pretty interesting, is its combination of FPS and RTS. Two races, aliens and humans (how innovative). They can make structures, however. You can use them for defense, healing, spawn points, even research and purchase weapons. Thats for a human. For an alien, every time you kill, the more you “evolve”
To win, you kill the enemy, and destroy spawn buildings.
Nice features:

16 buildings
buying weapons, armor, items, and multiple alien classes
scaling walls/ceilings
actual physics!
and…its free. 😀
and open source. happy downloading! its nearly 100mb tho. Here

its not as portable as say, phosphorus, but, hey…its a pretty innovative idea, and its free, so try it out.