Cube Puzzle
I didn't invent nor designed this part. It is just a kind of rebuild of the original of http://www.thingiverse.com/richgain
You can find it here:
http://www.thingiverse.com/thing:23279
The real original where richgain based his work on came from Iwahiro and can be found here:
http://puzzlewillbeplayed.com/444/IwahiroAIC/1/
Added some blends (10% & 20% of total object size) on the outer edges and removed any gaps between the parts. Therefore additional tweeking in your prefered slicer might be necessary.