BuddyPress User Circles

• Allow users to create circles of users(or lists of users).
• Filter activity by circles.
• Circle notifications.

And here is a list of all features for site admins:-

• Limit circle creation by roles.
• Configure if circle will be a top level tab or be managed under friends component.
• Restrict who can be added to the circle:- Friends or all members.
• Control circle privacy.
• Automatically create default circles for newly registered members.
• Control notifications for add to circle or remove from circle.
• Customize notification emails.