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
SelfCAD - SelfCAD is an online 3D modeling and slicing software.
MeshLab - System for processing and editing 3D triangular meshes, provides a set of tools for editing...
SketchUp - 3D for Everyone
Skanect - The Easiest Way To 3D Scan With the Structure Sensor and Kinect-like 3D Sensors