http://www.cs.washington.edu/homes/glinden/particleTree.html
Want the source? particleTree.java, a minor variation (on the right) particleTree2.java, and fPointTree.java. Don't expect a work of art, though.
The code uses a technique based (loosely) on particle systems. Neat stuff! This code could still use some tuning, though, since some of the things look a little to stringy to be trees. Still cool, though.
I have another applet that draws much better looking trees using an LGrammer algorithm. Pretty cool. It's right here.
glinden@cs.washington.edu