Thingiverse is a community to discover, make, and share 3D models. Users can download files of objects that others have made. Several of the objects can be customized and modified.
Morphosource is a project-based data archive that allows researchers to store and organize, share, and distribute their own 3d data.
Yeggi is a search engine to find 3D printable objects.
Open repository of digital files suitable for 3D printing.
Sketchup's design library of 3D models.
Collection of 3D models of various artifacts from the Smithsonian Museums.
Search, browse, download, and share 3D biomedical printable models including custom labware.
NASA's 3D resources site that includes several printable models in .STL format.
Site contains many 3D models of fossils. You can download an OBJ file to use in 3D printing.
Africanfossils.org has several 3D models of significant fossils and artifacts in categories such as hominids, animals, and tools. It is a partnership with Autodesk, National Geographic, the Turkana Basin Institute, the National Museum of Kenya, and Stony Brook University.
3D Scan project by artist Oliver Laric at The Usher Gallery at The Collection in Lincolnshire, UK.
3D scans of Native American artifacts from the Hampson Archeological Museum State Park in Wilson, Arkansas. OBJ files are included.
3D scans of artifacts at the British Museum in London.
Tinkercad has a free version of its software that creates 3D digital models. This is a great program for beginners and is used in the web browser.
Free design software that can be used as a web app, downloaded to PC or Mac, or as an iPhone/ipad app. This is a great program for beginners.
SketchUp Make is a free 3D drawing tool.
Blender is a free open source computer graphics software that can be used for 3D modeling.
Sculptris is a virtual sculpting program.
OpenSCAD is a free software to create solid 3D CAD objects.
Meshlab is an free open source program for processing and editing unstructured 3D triangular meshes.
Netfabb is a free software that processes and repairs stl files to prepare them for 3D printing.