Square Trace

You can track yours, your friend's or anybody's followings, followers and friends on Foursquare & Swarm.

Also who followed back to whom or who doesn't followed to whom is visible.

In free version, only user friends, followings, followers, people who followed back and people who following back and any users friends are reachable.

In paid version, you can add "any" users to your favorite list to reach that profile easily and you can see all interactions of any people in addition to her/his friends.