Stanford Encyclopedia of Philosophy (SEP)
Free online encyclopedia achieves what Wikipedia only dreams of
The Stanford Encylopedia of Philosophy could be thought of as the most interesting website on the internet. Not only because of the content, but also because of the site itself.
The SEP has managed to solve one of the internet's most fundamental problems, which is how to provide authoritative, rigorously accurate knowledge, and all this for free.
The actual knowledge contained in the SEP is sorted into neat categories where the world can go to learn everything that we know to be true, and it demonstrates a way for humans to become a lot smarter than ever before.
Because while it's true that the existing internet contains virtually all of the sum total of human knowledge, it seems that knowledge is buried under huge piles of speculation, opinion, and misinformation.