"Electric Sheep is a collaborative abstract artwork founded by Scott Draves. It's run by thousands of people all over the world, and can be installed on any ordinary PC or Mac. When these computers "sleep", the Electric Sheep comes on and the computers communicate with each other by the internet to share the work of creating morphing abstract animations known as "sheep". The result is a collective "android dream", an homage to Philip K. Dick's novel Do Androids Dream of Electric Sheep."
Electric Sheep gives you a really beautiful screensaver that is different every time you see it. I also find the technical aspects of this screen saver very interesting.