Previous discussion: https://news.ycombinator.com/item?id=7464896

RiteTag offers the world's first real-time hashtag grading system which aids users in modifying their hashtags to nail the ones most likely to get their tweets discovered by topic-opted-in audiences.

Browser extensions provide this goodness within Twitter for free users and for paying users, also in Hootsuite, Tweetdeck, Buffer, SocialOomph, and SproutSocial.