TapTalk.io - TapTalk.io is a complete in-app chat SDK and messaging API - Easy integration and customizeable.
Octopush - Octopush is a company providing technology-based communication solutions, including SMS, Web solutions, and Email APIs.
Lets Chat - Open source self-hosted chat app for small teams
Clearstream - Clearstream is a SMS marketing and online texting software.
MongooseIM platform - The massively-scalable XMPPJabber mobile messaging platform, for mobile and web, by Erlang Solutions
Swift SMS Gateway - SMS Gateway is your bridge between the Internet and the world of cell phone SMS text messaging.