Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Live Chat by Sumo.com - Instantly communicate with customers, prospects & visitors
Sonar - 2-way chat with your customers over SMS and FB Messenger
GoSquared Live Chat - Beautiful, simple, and free live chat for your website
ThroughMessage - Uncomplicated customer chat for ecommerce websites
Drift - A messaging app that helps you grow your business.