CyTube - Free, open source synchtube
myCircle.tv - Watch synchronized videos from Youtube, Dailymotion or Vimeo with your friends up to 20.
Metastream - Watch streaming media with friends
Kast - Kast is a social sharing platform where users can stream content from their computer to the people...
Watch2Gether - Watch2Gether is an app that allows multiple people to watch the same content simultaneously and interact with each other while watching.
SyncTube - A simple platform where you can create rooms, manage permissions and chat while watching YouTube videos synchronized with your friends.