Free meshmixer for Windows

A nice freeware application, which allows you to mix and match mesh geometry from different models. The video displays it better than I could in a short text.

Maybe the mesh topology (the clean edges and aligned series of edges) will suffer from it, but as a sculptural approach to modeling with library objects, it seems to function really well and smart.

Freely available but Windows-only.

Or to use the description from the owner:
meshmixer is an experimental 3D modeling tool developed by Ryan Schmidt, a computer graphics researcher at the University of Toronto who is also responsible for ShapeShop and some other stuff.