BuddyPress.org

It sounds like you would need create another folder in your root install of wordpress and title it something like “community”. Then create a bran-new WordPress install in the folder and then install BuddyPress. You’ll effectively have 2 WordPress installs. The one on your “main” site will just be what people look at. But the 2nd install in your community folder will be where people will create accounts, interact, i.e. basically everything else that BuddyPress does.