Freecad is one of the best Open Source 3D CAD programs available on the most popular operating systems (Windows, Linux, Mac OS). It is a fully parametric modeler similar in functionality to such programs as Inventor, Solid Works or Catia. With it, you can create simple 2D drawings, as well as complex models of entire objects or devices, and even buildings. It is difficult to list all of its applications, because there are a number of additions, that increase its basic skills.
The films are presented in the most intuitive way, and where it is necessary, comments were added. In the bottom right corner of each video there is a window showing the currently pressed keys and mouse buttons.
Are you interested in basics of Freecad ? Check basic course: http://freecadbasiccourse.com/