Engine: FaceBook

Docs features: Over 50,000 documents have been uploaded, including problems sets, poetry, lecture notes, and random funny stuff.

Every year, millions of college papers are produced, and virtually all of them are just gathering dust on people's hard drives. Too bad, because a lot of that is good stuff that other people would find useful. The point of Scribd is not to encourage plagiarism, but rather to help unlock the information on people's computers by making it easy for people to share their creations.