OSGeo uses a Mediawiki instance as our main wiki (http://wiki.osgeo.org).  The configuration of the mediawiki instance is documented here (in Trac) instead of in the regular wiki so that we have a decent chance of seeing this info if the wiki is down.  

 * Primary Maintainer: Martin Spott (Martin.Spott at mgras.net) (osgeo userid: "martin"). 
 * Host: "osgeo2" - the secondary system at Peer1 (ssh to wiki.osgeo.org or test.osgeo.net)
 * Configuration Location: /var/www/wiki_osgeo

It appears we also host the fossgis wiki (/var/www/wiki_fossgis).