OpenWiki has exactly the architecture which allows it to be plugged in the CocoonHive.org portal.
Each of its web pages can be served in a rich, presentation neutral XML format.
To make life even easier, OpenWiki conveniently provides XSLT stylesheets.
I have slightly modified the origninals to align them with the portal look and feel.
Some more work has to be done for the templates which handle editing a wiki page.
Thanks to Michael Cote for pointing out OpenWiki.