CyTube - Free, open source synchtube
Metastream - Watch streaming media with friends
Watch2Gether - Watch2Gether is an app that allows multiple people to watch the same content simultaneously and interact with each other while watching.
6IRCNet Synchtube - Synchronised videos and chat
Netflix Party - Netflix Party is an extension for watching Netflix remotely with friends and family for movies nights with that long-distance special someone.
Syncplay - Syncplay is a different kind of entertainment platform.