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
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
GoSquared Live Chat - Beautiful, simple, and free live chat for your website
Crisp Chat - Multi-channel customer support software
Drift - A messaging app that helps you grow your business.