/r/UniversityofReddit has been around for a while now and is up to over 8,500 subscribers (though our website has over 12,000 registered members).

The philosophy of University of Reddit is simple: there should be no barrier to entry into education, neither monetary nor geographic. Everyone should be free to learn. Everyone with experience in something specific should be free to teach, as long as they understand the commitment that they make and that they are subject to be asked their qualifications. We've had people volunteer to teach classes in typesetting with LaTeX, StarCraft II strategy (which evolved into weekly matches and a 1300 user reddit), starting your own business (still going on), puppy training, film theory, neuroscience, photography, topology (this one is still going on), and more - and hopefully even more in the future.

As far as I know, there aren't any similar reddits. The sidebar asks me to say why I think /r/UniversityofReddit should be promoted. The reason, in my opinion, should be that University of Reddit is the manifestation of an idealistic perspective on what the world could be like, a service that can do nothing but benefit, and that a lot of people would like to see it grow.