Grabcad.com. An online community for professional engineers, designers, manufacturers, and students to share CAD files and professional tips, participate in design challenges or download CAD models from the online library. The community has over 4 million members.
Thingiverse. Collection of 3D printed models, uploaded by users, and made freely available for others to use and customize. The various 3D objects files can be browsed via the explore tab on the website. Additionally, Thingiverse offers educational projects that are divided by subject area, such as art, engineering, etc.