Penguin Arena is a FPS (First Penguin Shooter). I currently own the demo, which you can play forever, and you can create/join a server and shoot other penguins. The best penguin wins!
There are three game plays. Teams (you and computer players against other humans/computer players!), Duel (1 vs 1 to 4 vs 4; depends on the # of players!), and Unlimited (Shoot an unlimited number of bonus!).
You can connect to the web or LAN network to play, or create a server with no multiply and battle against the computer alone.
If you buy the game ($20 and they donate $1 to Kiva) you can customize your penguin with different outfits and pick up bonuses (fish bombs, mega bombs, fish guns, and more, invincible, and bear claw feet).
You can even download custom maps and make your own in their map editor and post it on their forums for others to download!
Overall this game is very fun and perfect for something to do when you have nothing else to do.