TapTalk.io - TapTalk.io is a complete in-app chat SDK and messaging API - Easy integration and customizeable.
Rocket.Chat - Rocket.Chat is a Web Chat Server, developed in JavaScript, using the Meteor fullstack framework.
MongooseIM platform - The massively-scalable XMPPJabber mobile messaging platform, for mobile and web, by Erlang Solutions
CometChat - Seamless Real-Time Chat Integration for Your Applications.
Chat by Stream - Build and ship in app messaging in a few hours
Taskworld - Taskworld is a cloud-based collaboration platform that increases productivity, engagement at work.