Super-Ink applet
(Click and drag with the mouse to draw, hit space to toggle the control panel.)
Note: This project is still very much unfinished.
This is an expanded version of my ink dispersion system, made more flexible. (It's also probably somewhat slower.) It uses a tile scheme to avoid processing parts of the image that aren't "alive" which should enable it to handle much larger canvases. It has a GUI (toggled by the space bar) which allows you to edit the parameters.