Chris linked to this site, which has some of the prettiest Processing demos I’ve yet seen, and it inspired me to give it a go myself. The results aren’t quite so spectacular, but they are quite pretty nonetheless.
CityWander renders the paths taken by people as they walk across an empty square of land. If two individuals are about to collide, they will attempt to avoid collision by sidestepping. The starting points and directions are random, and the more a particular path gets walked along, the darker it becomes. The results depend on the number of individuals – but it generally produces a curiously organic looking texture which gradually fades to black. Click on the applet to restart it with a different number of people – the results will be quite different each time.
FractalPath was inspired by one of the examples on the Complexification page, buddha.brot. It renders familiar fractal sets – Mandelbrot and Julia – by tracing the paths of points leaving the set under the iterative functions of each set, again using an accumulative buffer. There are quite a few options on this one; the applet describes what you can do – play around with the options and you’ll get quite a wide range of very pretty pictures.
(if you’ve got a big, fast machine, you might like to try the bigger version of FractalPath)