As a Computer Animation student, I used MojoWorld a lot.
A little history: It was originally 'enhanced' by funding from NASA, as they wanted a program that was capable of modeling the immense surface data collected from satellites around Mars. My instructor for this course worked with Dr. Musgrave on producing the Mars model that NASA uses today.
Completely customizable, everything from the elevation bands of the terrain, to the number of moons the planet has. A trained 'flyer' can take you on a trip around 'your' world, many people do not know the true capabilities of this application.
It works seamlessly with Maya, for exporting terrain model segments, which can be used in Maya animated models as an environment component, which can be assigned as a static surface for use with fields, and sprites (i.e. rain, etc.).
MojoWorld is a fantastic program!