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Thank you for including Encyc in the Big Four. One correction about Wikipedia, though. Some people there are using their real names.
I'd also add Citizendium (complicated rules), Wikinfo (not sure how it's doing), and Conservapedia (active but ideologically narrow).
A good Wikiversity alternative is Wikademia.
Any blog or forum could also be a very good alternative. They're all instruments for communication, first and foremost.