Metastream - Watch streaming media with friends
CyTube - Free, open source synchtube
StreamParty - StreamParty is a watch communiry, that allows you to watch video streams in sync with the people you care about, on multiple services.
WatchParty.me - WatchParty.me is a video streaming platform where you can watch streams with your friends in a private virtual lobby.
Watch2Gether - Watch2Gether is an app that allows multiple people to watch the same content simultaneously and interact with each other while watching.
Netflix Party - Netflix Party is an extension for watching Netflix remotely with friends and family for movies nights with that long-distance special someone.