I originally wanted to combine the Leap Motion with the Blender 3D modeling software to create models using virtual hands. The limitations of the Leap and the lack of "open sourceness" of Blender made this much more difficult than I'd anticipated.
Instead, I used Unity. While much less focused on modeling, the game engine allowed more flexibility. I was able to create custom gestures and signals to simulate a 3D modeling environment, which was where I could be most creative.