SendBird - SendBird is messaging-as-a-service.

Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.

JivoChat - JivoChat is a live chat that enables you to talk to visitors on your website

Chat by Stream - Build and ship in app messaging in a few hours

tawk.to - tawk.to is a free live chat app that lets you monitor and chat with visitors on your website or from a free customizable page

Chatroll - Chatroll is the leading provider of interactive tools for social publishers.