Social interaction seems to be a hot topic for a number of major brands. Given the expertise in IT and programming from CAD vendors it is no surprise that many of them have jumped into social with their own community. Each of these is positioned to help designers and engineers share their knowledge, learn tricks, and get updates on their favorite (or most used) software, access crowd sourced files, and generally build a community of like minded designers.
2. Blender User Community
Blender: Complete tutorials, plugins, and forums to learn Blender from the ground up
3. Solid Edge Community
Solid Edge community: Questions and Answers regarding ST5 and ST6
4. Autocad Mosaic
Mosaic: Discussion boards, videos, and articles to maximixe Autodesk
GrabCAD Home: Library of model, tutorials, and design challenges