LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
FreeCAD - An open-source parametric 3D modeler
Sculptris - Sculptris: Enter a world of digital art without barriers.
SketchUp - 3D for Everyone
ZBrush - ZBrush is a digital sculpting and painting software solution.