Friendorfollow is a very simple Twitter web-based tool which does a few things: find out how many people are not following you back. As well as who is following you but aren’t being followed by you. You can then sort them according factors like Name, Location, Followers and even account age.
The best thing about it? You don’t need to log in or give away your password. Just enter your username and you’re done. It’s the fastest way to check who is not following you back.