Metastream allows you to watch internet videos with friends. It synchronizes media on websites so you can watch together.
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.
Syncplay program allows you and your friend/partner/family member to watch same video file simultaniously on different PCs and different location by syncing playback of MPC-HC, mpv, mplayer2 and VLC players.
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.
Web application that enables people to watch the same thing at the same time across the globe while interacting via video and text. Currently supports Netflix, Amazon, YouTube, Vimeo, Crunchyroll, etc.
Kast is a social sharing platform where users can stream content from their computer to the people in their channel (called parties). Kast parties allow up to 20 people to share their screens and up to an additional 100 people to view in the party.
SyncPlayer is an unofficial open source Syncplay client for Android. It connects to Syncplay servers to sync video playback between two or more users. Use it to watch videos with your friends online.
Watch YouTube collaboratively with others online, synced to the second! Create your own room and join a room and invite others.Warning
Contains the coin miner CoinHive. See https://www.virustotal.com/#/url/4757e4e2c0858ae55b604687189e765ac3bb2fc276daa31f61c6aa73c0474230