planetGenesis

planetGenesis (pG) is a Java program designed to produce models of planets and landscapes.
A little like Mojoworld but free (as in beer and speech) and no where near as good.
You can see a movie of pG in action here

pG produces -

• 16bit greyscale bitmaps.
• Wavefront format objects.
• POV-RAY 3.5 mesh2 meshs.
• Terragen terrains.

and this