From Carl Davidson, the creator of PyTectonics, a javascript-based plate tectonic simulator with movement on a spherical surface.

This is something I would have done myself a long time ago if I wasn't such a crap programmer. This runs reasonably fast even on my nearly six year old Macbook even in Safari. It has equirectangular* output and 8-bit land-only elevation output as well.

Development is ongoing, and Mr. Davidson seems to be responsive to suggestions.

I have a blog with a very basic tutorial on the use of the program.