The objective of this particularly fun looking game is to guide a ball along a path and hit different elements on the way at the beat of the song. It's accelerometer-controlled and for the rest, it's pretty straight-forward, the better you stick to the track, the more points you make and if do poorly, you lose the music.
The game is $3 and comes packed with three songs from the Black Eyed Peas, further songs can be then acquired inside the app. Here is Riddim Ribbon's demo from Apple's keynote five months ago:
And here is the official trailer: