MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
Blender. Sphere + Subdivide (a lot) + Displace Modifier + Musgrave Texture (possibly multiple passes, lots of tweaking parameters). I think I used Voronoi F3 for the texture basis, but I'm not sure. I started with a sphere I had added a little texture to manually with MeshMixer. I also reduced the polygon count with MeshMixer afterwards so that the file sizes were easier to work with.