I came across this interesting website:

101 Free Open Course Classes to Learn How to Build ANYTHING

What are open course classes? Basically, they are all the materials of a college class made freely available to anyone online: the syllabus, handouts, lecture notes, assignments, etc. If you were so inclined, you can use this to take the class on your own. Obviously, you lack the feedback and interaction with a professor, and it does not count toward any certification or degree, it can be a great resource for self-education in a more structured way.

Most of these classes come from MIT, which pioneered the open course class idea, but more universities seem to be jumping in on the bandwagon. This list has some fairly high-tech classes (holographic imaging, bioengineering, and space propulsion), but there are some others that seem interesting for a props artisan or other theatre practitioner, such as intro to stagecraft, scenic and costume design, and furniture making.