Here is a simple particle system animator I wrote for fun. The idea is that the applet contains a source of glowing particles which are ejected at a given angle and amoount of spread. The source of the particles may be at a point or spread over an area. Other options include adding gravity and random kicks to the motion of the particles. After each frame, one or more image processing operations are applied to the image. Finally, a suitable color map is used to display the images.
You will need a fast machine to get any speed out of the animation if you turn on too many operations at once.
This applet requires Java 1.1, so users with older browsers will be out of luck :-(
If you want to play with this, here's the source. It requires a couple of classes from the filter library to create the colormaps, but you could quickly hack up your own colormaps instead. [I'm not allowed to release the source of the filter library at present]
Here are a few example particle animations which used to be on this page.