FlexWiki: Microsoft's latest Open Source project has some very cool features including... "Federation and namespaces - When there are many somewhat related Wiki sites, it's often hard to get them to link together smoothly. FlexWiki has some very cool features to support this scenario. Specifically, a single installation of FlexWiki (called a WikiFederation) can bind together multiple WikiBases. All topics in a WikiBase live in a TopicNamespace. See WikiFederationOverview. "