What? inCommon allows you to find common friends and followers on Twitter.

Simply enter two Twitter usernames and inCommon will match them to find people who follow both of them, and people who they both follow.

When you’ve found matches, you can follow/unfollow them, find matches for them, and open them in your favourite Twitter app (Twitter, Echofon, Tweetbot and Twitteriffic are currently supported).

See The App