Thirty small red balls are bouncing around the iPhone's screen, making sounds when colliding with the walls. The balls are more or less following the law of physics. Individual forces are calculated using the real world acceleration data provided by the iPhone. This means that you have to tilt the iPhone to get the balls moving. Stoke's friction is applied to prevent them from going too fast. In summary the app behaves like there is a fluid behind the glass of your iPhone's screen with thirty red little balls moving through it.
What's the use of this app?
Well, not much! Just play around with it and be impressed about your iPhone being able to calculate forces and collisions. Maybe you can even relax while doing so! And please show mercy with me: It's my first app and I am a physicist. ;-)