This open-source app displays 50,000 particles attracted to up to 5 points that you can move with your fingers.
You can adjust most of the parameters in the settings menu (tap on the top right corner to display the rotating gear, then tap on it to display the settings menu).
You can also use Particle Flow as a live wallpaper!
Inspired from the following project: https://code.google.com/p/renderscript-examples/wiki/Gravity
Particle Flow Screenshots