What are some alternatives?
PubNub - PubNub is a real-time messaging system for web and mobile apps that can handle API for all platforms and push messages to any device anywhere in the world in a fraction of a second without having to worry about proxies, firewalls or mobile drop-offs.
Pusher - Pusher is a hosted API for quickly, easily and securely adding scalable realtime functionality via WebSockets to web and mobile apps.
Firebase - Firebase is a cloud service designed to power real-time, collaborative applications for mobile and web.
Socket.io - Realtime application framework (Node.JS server)
Scaledrone - Realtime messaging service
Lightstreamer - Lightstreamer is a server for delivering real-time messages to browser-based and mobile...