[@danbp Participant 13 years ago]

Actually you can use BP 1.8.1 with bbPress 2.4 to get what you want.

Since BuddyPress 1.6, bbPress is no more attached to BP groups and can be installed as a standalone full, complete, forum
3 types of install are possible: goup-forums only, single forum only or both.

Read here please.

Installing Group and Sitewide Forums

bbPress