Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Autodesk DWG TrueView - Get a free DWG viewer to view, open, edit, and convert .dwg files, the native file format for AutoCAD files. DWG Trueview includes DWG TrueConvert.
Sculptris - Sculptris: Enter a world of digital art without barriers.
Autodesk Design Review - Design Review lets you view, mark up, print, and track changes to 2D and 3D files.
Sketchfab - Sketchfab is an industrial design software tool is useful for ideation and for beginners in the industrial design field.
ZWCAD Viewer - Cross-Platform .DWG | .DXF | .DWT R12-2013 Viewer