I designed this in Tinkercad. It's a one-print hollow cube with a ball inside that can roll freely inside the cube. The ball is larger than the holes in the cube making this impossible to make any other way while keeping the cube in one piece. The included file has several different variants that can all usually be printed on a desktop printer with supports and a raft.

Note: I printed with the file titled "Original Cube Sphere" but I recommend using the one titled "20k Cube Sphere." Update: New hd models! The extreme high poly version uses Kazzee's Sphere with 20k facets http://www.thingiverse.com/thing:156207

My examples have a few minutes worth of breaking supports and sanding to get where they are now. The file has the models at about 75 mm but mine were printed at 30 and 32 mm each.

MakerBot

MakerBot Replicator

Yes

Yes

15

Break supports and raft, then sand and you're done!