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