MatrixCombined/SRW


 * Wikis
 * Usenet
 * Wikipedia
 * Internet Archive
 * Couch Surfing
 * Hospitality Club
 * ibiblio.org hosts many services both r/o and r/w as contributors deem appropriate.
 * Del.icio.us
 * Netscape
 * Metafilter
 * Wikia.com (a hybrid with the commercial section)
 * SecondLife (just announced its client code will be GPL'd
 * H-net and other academic discussion lists