Flock is a relationship manager built on Twitter. We've been quietly beta testing viewing Unfollowers and we're finally done! It actually turned out to be one of our most retentive features: people love it and the announcement seems to have driven a large number of signups on its own.
Our idea was that this would be very useful for brands trying to know who to re-engage in the event of an unfollow. Next up we're actually going to raise prices in the coming weeks; we're going to grandfather everyone at the price they signed up at– but we suspect we are charging way too little given the feedback we've been getting.
Check out Flock at https://www.flock.network