I was just going through a few wallpapers and was impressed by Fractal's. A fractal is a geometric shape that in a part is made up of a smaller but similar shape. More about it here.
Wanting to try a few fractals I googled up and stumbled up on fractalview. Downloaded it from sourceforge and tried it. Its a java based so just had to set the classpath and ran it.
Fractalview is a java application for viewing a few common fractals ( Mandelbrot set, Julia set). It runs in a fullscreen mode showing up a fractal. By using different keys you can change the parameters like julia constant, colors or do a zoom and even save it as a PNG file.
Few fractals I captured are here.
The fractal view gallery has some good ones.
Gimp has also got a very good plug-in for generating fractals called as fractal explorer It happens to be the easiest and best one I ever found.