I think you may be thinking of a MIXED application.
I have an example at:
http://seahawk-forum.968426.n3.nabble.com/(It's a boating site rather than a locality/community site, but the top-level application is MIXED and most of the sub-forums a FORUMs, though there is now one sub-sub-forum that is a customised GALLERY. )
Others Administrators do something similar with a CATEGORY or BOARD application at the top level. (The CATEGORY application can be particularly useful for some as it places a sub-forum's Description field under the name of the sub-forum when you view the top level application.)
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.