The sum total of these Wiki sites about various XML and related topics go some way towards realising Mike Champions idea of an XML Wikipedia. Obviously there's a hell of a lot more to do, but tying together whats around already is a good start.
- CocoDocoWiki -- the Cocoon Documentation Wiki
- RDFWeb Wiki -- a Wiki to accompany the RDFWeb website, IIRC channel, and rdfweb-dev mailing list. Various RDF related topics, including FOAF
- SVGWiki -- Wiki about SVG
- DocBookWiki -- Wiki for DocBook related information
- XML entry on Wikipedia -- the entry for XML in the real Wikipedia. Links to various entries to other XML technologies
- XML related pages on C2 Wiki -- search for XML related pages on the C2 Wiki
- RESTWiki -- for discussions about REST
- Python XML-SIG Wiki -- for collaboratively developing documentation for the PyXML package
- Zope XML -- XML in Zope discussions
- XML Wiki -- derived from the EFnet #XML IRC channel. Looks to be obsolete.
- BioXMLWiki -- again, looks obsolete