Socket.io - Realtime application framework (Node.JS server)
Aircall - Aircall is a call center software of a new generation designed for fast growing companies. Setup instantly and integrates to your CRMs
Ably - Serious realtime infrastructure
Ameyo - Ameyo is a powerful and highly flexible IP-based contact center software that lets you have a personalized interaction with every customer across multiple channels, thereby driving customer engagement to a level par excellence.
Pusher - Pusher is a hosted API for quickly, easily and securely adding scalable realtime functionality via WebSockets to web and mobile apps.
Five9 - Five9 provides cloud-based call center software for sales, marketing and support.