Lithoshpere is a node based terrain generator using python and your GPU. [ame]http://www.youtube.com/watch?v=VE4bbDM5MV0[/ame] It appears to be able to export meshes, heightmaps, and textures. Requires Python 2.6 - 32bit, and a relatively beefy GPU. Looks like it runs on Windows, Linux, and possibly even Mac...