TapTalk.io - TapTalk.io is a complete in-app chat SDK and messaging API - Easy integration and customizeable.
Viber - Free and secure calls and messages to anyone, anywhere. Keep your conversations going no matter where you are.
Lets Chat - Open source self-hosted chat app for small teams
MiVoice Business - MiVoice Business is a business communication platform that delivers voice, messaging, mobility, presence, conferencing, collaboration and applications.
WeChat API - WeChat API and SDK allow developers to access and integrate the functionality of WeChat with other applications.
Screenleap - Screenleap is a web app that lets users share their device's screen over the Internet. These screens can be a desktop computer monitor or a smartphone screen or anything else that can load a web browser. Read more about Screenleap.