Wikis

web sites
users can create new pages/change existing pages easily via HTML user interface
original WikiWikiWeb: no access control, everybody can participate
Mr. D.I. can participate in the CfP specification effort
people occasionally vandalize wikis (recovery is easy: revert to last version)
no wikis available to date that export RDF data (wrong! Platypus wiki was posted yesterday on #rdfig weblog)