Blender - Blender is the open source, cross platform suite of tools for 3D creation.
MakeHuman - MakeHuman is a free, open source, interactive modeling tool for creating custom 3D human characters.
FreeCAD - An open-source parametric 3D modeler
ZBrush - ZBrush is a digital sculpting and painting software solution.
Sculptris - Sculptris: Enter a world of digital art without barriers.
meshmixer - meshmixer is an experimental 3D modeling tool for making 3D mashups without too much hassle.