Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Sculptris - Sculptris: Enter a world of digital art without barriers.
FreeCAD - An open-source parametric 3D modeler
Sketchfab - Sketchfab is an industrial design software tool is useful for ideation and for beginners in the industrial design field.
ShapeShop - ShapeShop is an advanced and professional 3D design and modeling application that comes with an easy-to-use and user-friendly interface.
meshmixer - meshmixer is an experimental 3D modeling tool for making 3D mashups without too much hassle.