FreeCAD Parts library
There is a little side-project to FreeCAD, which aims at collecting reusable objects under a creative commons license, that we are currently hosting at https://github.com/yorikvanhavre/FreeCAD-library . It features a small browser integrated into FreeCAD, but can also be used with other applications, since all objects are also stored as STEP files.
It currently doesn't contain a lot of objects, but it grows slowly. If you wish to contribute with some objects, look at the readme file on the repository above for instructions.