Community Kit for Sharepoint
The Community Kit for SharePoint is a set of best practices, templates, Web Parts, tools, and source code that enables practically anyone to create a community website based on SharePoint technology for practically any group of people with a common interest.
Codeplex link -> http://www.codeplex.com/CKS
Demo -> http://sharepoint.microsoft.com/sharepoint/cks/uge/default.aspx
