[xwiki-users] Developing Discussion Forum using xwiki?

Hi Folks, Looking at extensiility of xwiki, i am looking to make a typical forum application on top of xwiki. The forum will be basically a discussion forum where each user will be given user id and password. There will be pre-defined topics like Realestate,Sale-Purchase,miscellaneous,etc . Each user can start a thread on any forum and continue the discussion. It would be a great help , if some can point me to reference project where similar stuff has been done or guide me how to start with? Thanks in advance.