Electric Sheep is a screensaver, open source, cross platform, and free. However, it uses distributed computing of a sort to generate massively complex fractal animations that grow over time, and evolve in complexity. It's impossible to describe the images created. You can view a gallery here. The best images take several hours to generate, but they are worth it. There are music videos with the Sheep, a high-def version, and you can get more Sheep via Bittorrent. All cool neat eye candy.