Blender - Blender is the open source, cross platform suite of tools for 3D creation.
FreeCAD - An open-source parametric 3D modeler
SolidWorks - Dassault Systèmes SolidWorks Corp. develops and markets 3D CAD design software, analysis software, and product data management software. SolidWorks is the leading supplier of 3D CAD product design engineering software.
Sculptris - Sculptris: Enter a world of digital art without barriers.
LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
meshmixer - meshmixer is an experimental 3D modeling tool for making 3D mashups without too much hassle.