Metastream allows you to watch internet videos with friends. It synchronizes media on websites so you can watch together.
StreamParty is a community, that allows you to watch video streams in sync with your friends all across the world, on multiple services, right on their website.
OpenTogetherTube lets you watch videos with your friends as easily as possible. It's completely open source, and able to be easily self-hosted via provided docker images.
Kosmi is a free real time application and communication platform that offers voice, text and video calls along with games and applications such as SNES Party, NES Party, OpenArena, Poker, Virtual Cardtables, Synced YouTube and Cowatch Video.
Watch2Gether lets groups of users watch videos in-sync together. At the same time users can communicate through a build-in chat-room and use web cam and audio chat. Available media sources are Youtube, Vimeo, Dailymotion and Soundcloud.
Netflix Party is a Chrome extension for watching Netflix remotely with friends, e.g., for movie nights with that long-distance special someone. It synchronizes video playback and adds group chat.
Rave is a free iOS and Android application where you can watch Netflix, Disney+, YouTube, Prime Video and more with friends while chatting in perfect sync. Rave is also available on Chromebooks, Android TV, and is coming soon to Mac and Windows.
The social music experience! Play and discover music LIVE with your friends and other Beatsters around the world.