Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
The Big Book of Churn - The definitive guide to customer churn reduction
indemandly - Live chat 2.0: Customer messaging that converts
Customer.io - We make it easy to send emails triggered by user behavior. Build, measure and improve your emails to activate and retain users
Twixor - Customer communications made interactive and dynamic!
Postmark - Postmark is the easiest and most reliable way to be sure your important transactional emails get to the inbox. Simply & reliably parse recieved email to JSON for your webapp.