ilo - Premium Twitter analytics
Accountanalysis - A tool to evaluate Twitter accounts
ClockTweets - Schedule, analyze, and stalk challengers on Twitter
Secateur - Use Secateur if you want to temporarily or permanently block or mute (or both block and mute) a Twitter account and all its followers.
Followerwonk - Followerwonk by Moz is a Twitter analytics tool to help companies better understand their Twitter followers.
LessNoise - Recommendations on who to unfollow on Twitter