Freshdesk - Freshdesk is a cloud-based customer support software that lets you support customers through traditional channels like phone and email, social channels like Facebook and Twitter, and your own branded community
ClearBrain - Predict which users will upgrade or churn tomorrow.
Maian Support - Free responsive PHP Helpdesk System
ChurnBuster - Stop Losing Money toFailed Payments in Stripe. Churn Buster saves you thousands of dollars every month by ensuring your customers update their payment information.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
ChurnKit - Find out who removed your service from their website.