I know of Khan Academy. I talked about a bit on Murray's World in 2012 I think but no one said much about it so I didn't want to go on about it. Bill Gates is well into it as I believe he's one of the primary resources/donators. I listened to some of Salman Khan's lectures on youtube. Very good stuff. Salman is doing a world of good out there with no costs.
I had heard about Khan Academy a long time ago, but it was from teachers. I got the impression that it was a tool for them and K-12 students. I didn't realize that anyone could use it as a learning tool.
It has such a wonderful set up. I introduced my son to it, and even he thought it was cool.