Top Draw is an image generation program. By using simple text scripts, based on the JavaScript programming language, Top Draw can create surprisingly complex and interesting images. The cool part is that the program has built in support for taking your image and installing it as your desktop image. There's even a Viewer application that can be installed in the menubar to automatically run with the parameters (such as the selected script, update interval) that you've specified.

Mac OS X 10.5 (Leopard) or later.

There's also a Google Groups page for the project: https://groups.google.com/group/topdraw