CavePainting
CavePainting is a relatively simple but powerful program for sketching 3D models in virtual reality. As opposed to more traditional CAD or animation style 3D modeling programs, CavePainting is easy to learn and is focused on exploring a style of computer graphics driven by hand-based input, like drawing or painting.
Running CavePainting
Config Files
Interacting with CavePainting
See the Use Cavepainting HOWTO.