TapTalk.io - TapTalk.io is a complete in-app chat SDK and messaging API - Easy integration and customizeable.
Lets Chat - Open source self-hosted chat app for small teams
Telegram API - We offer two kinds of APIs for developers. The Bot API allows you to easily create programs that use Telegram messages for…
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
Twilio - Brings voice and messaging to your web and mobile applications.