The Sun Project Interactive
The goal of Sun Project Interactive is able to very quickly generate images that look vaguely similar to Space imagery that comes out of NASA. At present the project is able to generate nebula like images, simple star-fields and suns.
This was a project I created many years ago in high school. I haven't really touched the code since then, but still use the program on a regular basis to create the backgrounds for many of my sites & profiles. I never got around to porting it to Linux, but it runs just fine under wine.