Socket.io - Realtime application framework (Node.JS server)
Smart Tab Mute - Ensures that only one tab is playing sound at the same time
Pusher - Pusher is a hosted API for quickly, easily and securely adding scalable realtime functionality via WebSockets to web and mobile apps.
MuteTab - Better tab muting in Chrome
Ably - Serious realtime infrastructure
Dead Simple Screen Sharing - Simple screen sharing and audio conferencing software.