Socket.io - Realtime application framework (Node.JS server)
Apache Tomcat - An open source software implementation of the Java Servlet and JavaServer Pages technologies
Pusher - Pusher is a hosted API for quickly, easily and securely adding scalable realtime functionality via WebSockets to web and mobile apps.
Microsoft IIS - Internet Information Services is a web server for Microsoft Windows
Ably - Serious realtime infrastructure
Apache HTTP Server - Apache httpd has been the most popular web server on the Internet since April 1996