Companies on this[1] or this[2] list. A lot of what these companies provide (I worked at one) is merely a way to gain insight into your social media profile. Twitter Analytics is an extremely good implementation of this service for free. Twitter also gives you the CSV to mine your own data allowing an individual or company to make correlations that Twitter might not necessarily be able to make.

You're right, Twitter may buy some of those companies but to me, that's still out of business.

[1] - https://business.twitter.com/partners/list/certified-product...

[2] - https://business.twitter.com/partners/list/marketing-platfor...