FollowerWonk is a paid social media tool for Twitter. This tool gives a wide variety of information about the followers of a given account and about the account’s activity on twitter. This can be very useful to assess the demographics of the follower base of a given account.
FollowerWonk has a proprietary metric called Social Authority. In their own words: Social Authority helps you find, optimize, and engage your Twitter audience. It’s a 1 to 100 point scale that measures a user’s influential content on Twitter. More than just another self-focused metric, Social Authority helps you discover influential tweeters.
FollowerWonk can be used to track follower activity in Twitter. This is an example of a timeline of new and lost followers. This can be very useful to evaluate results of social media campaigns or types of content posted
In conclusion FollowerWonk is an excellent resource to track metrics of activity in Twitter.