This is the classic mechanical maze and marble toy game brought up to the iPhone times.
There are concentric circles with a single entrance between each circle and the next. There is a set of marbles(max 12, default 1).
The objective is to tilt the iphone in different directions so as to roll the marble in the desired direction - the effects of gravity will roll the marble when the iphone is tilted. Continuous smooth manipulation is required to move the marble in the right direction.
The marbles slightly repel each other(actually small variations in gravity cause them to collide and after collision they slightly move away from each other). Whenever a marble hits the partition in the ring, again, it will be slightly repelled.
You will need to be deft and maneuver the marble at the right angle and speed to get it through circles and gather all of them at the center of the maze.
To change the number of marbles, press 'i' at the bottom of the screen. You will brought to the screen which lets you set the number of marbles. After setting the number of marbles, you can get back to the play by pressing 'Done'.