3 saves http://blog.samgerstenzang.com/post/110452097098/knowledge-units
There are two models of online education: 1. Preparatory knowledge, in the form of course-based video-delivered teachings: Coursera, Udacity, Thinkful, etc. 2. On demand knowledge: Wikipedia, StackOverflow, Genius, etc. Of the two, the latter has been much more widely spread and far more influential.