BuddyPress.org

s2member is great if you want to require payment to access the member only site.

Absolute Privacy looks like it just requires a login to get to any pages.

@r-a-y had some code in a past thread (https://buddypress.org/community/groups/how-to-and-troubleshooting/forum/topic/members-only-2/#post-52901) which I believe will just redirect all pages to the login page if you’re not logged in already. Simple solution