Revit Server is available thru Autodesk Subscription. It allows multiple users in seperate offices to access the same file. This is different than traditional Worksets. There are some specific requirements to have inplace forthis to work. IIS7, Windows Server 2008 (not r2), and this only works presently within your WAN.
This is a good link to Autodesk's website regarding Revit Server, and it has a few videos as well: http://usa.autodesk.com/adsk/servlet/ps/dl/item?linkID=9243099&id=15731389&siteID=123112