An unfollow tracker is an application that lets a Twitter user know if his account has been unfollowed. These applications also include other services, such as a tweets timeline analysis or a historical graph to show progression of follower growth.
Some of the applications that provide unfollow tracking are TwUnfollow, Twitter Counter and TweetEffect. TwUnfollow provides basic tracking information, and it is also able to provide email alerts when an unfollow occurs, including the identity of the unfollower. Twitter Counter, on the other hand, is a data trending site for overall follower database as well as prediction models based on historical data. TweetEffect provides a separate functionality tracking any follows or unfollows and associates them with a tweet that was made at the time.