A community-built and maintained database of science fiction, fantasy, and horror that includes bibliographic data, community reviews, ISBN numbers of as many editions as people can find (of use to amateur librarians such as myself), and links to anthologies.
A grassroots peer-based education project based around online learning and remote collaboration between small groups of students. They just started up so things are a little thin at the moment. This is an interesting experiment to keep your eye on. Creative Commons.
A wiki about international travel by international travelers. Talks about many different destinations, specific places and times you might want to visit, airports, local travel, things to do, food, telecommunications, and safety.