Well 9rules essentially changed the term "forum" into "community".
They just hacked bbpress to take away the word "/forum/" in the urls for the pages.
Each of their "communities" is simply a forum, perhaps with a different style.css to make it look a little different.
You can edit any of your templates to put specific links to any of your forums. If all you want is simple color and minor style changes, you don't need a theme switcher, you just need to load a supplemental style.css based on the forum (or topic within the forum).
I think I can whip-up a new plugin to add the additional style.css based on forum number. But the important question is if you know how to use css and make it do the style changes you want? Because that would be a project-stopper if you don't know how.