Uzu Visualizer
Uzu is a unquie and wonderfully entertaining iPad app. Technically speaking, Uzu is a kinetic multitouch particle visualizer. You basically get a different visual effect for ten points of contact. The developer plans on updates to add different effects.
Here are the 10 Modes of Control
0 Touch: Brownian motion and boundary wrap
1 Touch: emanate and radiate
2 Touch: pinch attraction and boundary bounce
3 Touch: tri-point vortex
4 Touch: quad-point inverted vortex
5 Touch: 3d freeze and translate
6 Touch: 3d oscillating mass
7 Touch: 3d tri-arm spiral
8 Touch: 3d warp and inverted translate
9 Touch: 9 springy space ribbons
10 Touch: change color and particle size