using budypress for other blogs on different domains

1. my main budypress installations is on
2. I have other domains that are linked as subdomains to my main domain
3. one such domain is
4. i want to use forums, groups offered in BudyPress for my domain
5. I understand that I cannot use Forums nor Communities on any of my subdomains because they are incompatible with BudyPress.
6. What other plug ins or solutions do you recommend so that I can use groups and forums for

thanks and I eagerly await your response to this post