You should read the Administrator's Guide on my GregHelp forum:
http://greghelp.991552.n3.nabble.com/Administrator-s-Guide-f4012830.htmlThat explains not only which of the apps include the feature you request by default but also how you can implement it on any Nabble app you decide to use.
If anything still does not make sense post a question here and I will attempt to clarify the point.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.