Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Online 3D Model Converter - free online 3D model converter, upload a model and export it into popular formats
FreeCAD - An open-source parametric 3D modeler
Skanect - The Easiest Way To 3D Scan With the Structure Sensor and Kinect-like 3D Sensors
meshmixer - meshmixer is an experimental 3D modeling tool for making 3D mashups without too much hassle.
3D Object Converter - 3D Object Converter, a powerful 3d polygon model translation and interactive viewing shareware tool...