Blender - Blender is the open source, cross platform suite of tools for 3D creation.
LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
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.
SketchUp - 3D for Everyone