MeshMixer is an experimental 3D modeling tool.
The goal of meshmixer is to make it dead easy to compose new 3D models from existing meshes. You can cut, mix part of different 3Dmodels.
All the operation are done by easy drag and Drop operations. The only drawbacks is that the software only works on Windows.
Here an example (Create a minautore from a Human Body and a Cow head) :
Additional Help : Here