Login to your XWiki from social sites (FB, Twitter, Foursquare, etc.). Based on socialauth
Support SAAS remote user based SSO authentication and get informations from LDAP server.
Enforce some limits on an XWiki instance: number of users, number of wikis, etc...
IRC Bot (logging, wiki page notifications, wiki search, jira search, jira URL creation, and more)
Allow you to create Flash messages aiming at one or multiple local groups
Content templates that provide a certain structure for pages, making it faster for users to follow a certain layout standard