Blender - Blender is the open source, cross platform suite of tools for 3D creation.
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.
3D-Coat - 3D-Coat is the one application that has all the tools you need to take your 3D idea from a block of digital clay all the way to a production ready, fully textured organic or hard surface model.