TapTalk.io - TapTalk.io is a complete in-app chat SDK and messaging API - Easy integration and customizeable.
RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies
Lets Chat - Open source self-hosted chat app for small teams
Dialpad - Switch is a cloud-based phone system built for Google Apps users.
WeChat API - WeChat API and SDK allow developers to access and integrate the functionality of WeChat with other applications.
Aircall - Aircall is a call center software of a new generation designed for fast growing companies. Setup instantly and integrates to your CRMs