I have recently started following a free online physics course taught by Ramamurthy Shankar at Yale; sometimes I find I don’t understand the maths, so I turn to the Khan Academy to get up to speed. (eg on calculus). The Khan Academy site has a graphic ‘web’ connecting different elements of mathematics, so you can study what you will need to know before you go on to learn the bit you want to know.
This is an excellent learning structure for maths and the hard sciences; but I think it could be used, suitably modified, as a model for all the different subjects for which there are good learning resources online; a kind of Global Learning Net, built as a Wiki.
There are many sources of learning freely available online, and more are being added every day. In addition to the college-based projects like Coursera, there many others, eg Khan Academy, BBC Bytesize, which teach subjects from a much more basic level.
And then there are other, less academically-formal sources of knowledge; free-to-read textbooks in PDF, TV documentaries, well-informed debates and discussions programmes, available for example on Youtube.
What is needed is a kind of directory/guide, enabling anybody with access to the net to study anything they want to study, whether as part of some formal academic course, or for their own personal interest. Such a guide would also be very useful to professional educators.
All of these free sources of knowledge could be linked as elements in a net, with two kinds of arrows attached to each element; one sort of arrow (green?) suggesting more advanced elements on the same subject, and another sort of arrow (red?) pointing to some more basic elements.
Using a Wiki structure, any suitably knowledgeable contributor, happening upon a relevant resource, would be able to attach some (red and green?) arrows to that resource, thus linking it into the net.
I have at present no clue how to establish a Wiki capable of growing into a Global Learning Net, but I would love to hear from anyone who does!