Followers on Pinterest lets users take an anal retentive approach to their friend lists. Among other features, the program lets you not only see who has unfollowed you recently, but keep track of everyone who has ever unfollowed your account. (Great for holding a grudge.)
According to prMac, it is the only Pinterest app that currently provides this service. In order to drum up a userbase for the application, Innovatty is offering it up for free Monday only, after which it'll cost $1.99.
Followers on Pinterest is the logical next step behind apps like who.unfollowed.me for Twitter and tumblr.friendorfollow.com for Tumblr. But it's also a veritable Pandora's Box of passive aggression. Pinterest is a unique service because it focuses on stuff, not people.