Shrapnel is an extremely simple and extremely addicting app. Your goal is to dodge all the "shrapnel" on screen and see how long you can last. Use a mixture of jumps, crouches, and running to maximize your time. Grenades drop increasingly more often as time progresses making it harder and harder to survive.
This app is made with cocos2d. Check it out at http://www.cocos2d-iphone.org/