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
Bforartists - Bforartists is a fork of Blender.
Sculptris - Sculptris: Enter a world of digital art without barriers.
Art of Illusion - Art of Illusion is a free, open source 3D modelling and rendering studio.