BuddyPress.org

I’m also looking for this exact solution. But in the meantime, I’m thinking about using 3 separate installs: The “main” page would be a normal WP install that would highlight activity from two buddypress blogs (members wouldn’t sign in here). The two separate installs would be BP installations (my group wants distinct styling for each of these BP installations): all I want to do is share users and login credentials between the two BP installations.