There are two models of online education

Sam Gerstanzang:

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.

What works about on demand knowledge is that it is pull based (the knowledge you need, when you need it) and comes in digestible chunks. Unlike MOOCs, which are consumed far in advance of the knowledge being applied, Wikipedia and StackOverflow are the knowledge you need, now. Humans are lazy and working ahead requires discipline and foresight, which makes on demand knowledge far more appealing to most.