BuddyPress.org

Read this post I made on the bbPress forums:

https://bbpress.org/forums/topic/bbpress-vs-buddypress-or-in-addition-to-it-a-newbie-has-questions#post-65097

Yes, bbPress is necessary if you want group forums.

You might want to read this post by Boone Gorges as to what he did to transfer an existing bbPress install into BP:

http://dev.commons.gc.cuny.edu/2009/12/06/upgrading-from-buddypress-1-0-to-1-1/

Another bbPress to BP guide is available here:

https://buddypress.org/forums/topic/completely-integrating-a-previous-bbpress-install

I think I might add this to the FAQ