Socket.io - Realtime application framework (Node.JS server)
UserGuiding - User onboarding made easy, for less. Create product walkthroughs in a couple of clicks, without breaking the bank.
Pusher - Pusher is a hosted API for quickly, easily and securely adding scalable realtime functionality via WebSockets to web and mobile apps.
Usetiful - Fight user churn with great user onboarding. Interactive product tours and smart tips significantly improve your user retention.
Ably - Serious realtime infrastructure
Userlane - Digital adoption platform with interactive guidance for software applications allowing anyone to understand and master any software from the get-go.