Chris Allen has done a fine service with a history of social software, tracing the origins of today's networked communication back to the ideas of Vannevar Bush and Doug Engelbart, and several generations of computing platforms. The piece has been gathering additional references and suggestions: Pete Kaminski adds references to the 70s and 80s bulletin board era.
Jon Lebkowsky thinks he should write a book.
Seb Paquet's been wanting to make a wiki
Shelley Powers is building here.
A timeline on the Many to Many wiki.
This calls for a good BarnRaising.