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.
OpenTogetherTube vs CyTube opinions
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.
Enjoy movie night online with your long-distance partner, start a watch party with good buddies, or hang out and binge anime with your best friend. Hyperbeam helps you stay close, even when you’re apart.
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.
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.
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.
Watch videos together with friends. Chat and react in real time to a synchronized stream, with multiple ways of watching video, including screenshare, VM, and YouTube.
Invited.tv is a online video streaming service that allows friends to host watch parties using virtual browsers. Invited allows users to take turns controlling the virtual browser to easily browse and surf the web.