Zimmer is described as 'Enjoy YouTube Music Together: zimmer is the easiest way for friends to chat in private rooms while watching YouTube videos. Gather your friends and turn any YouTube video into a virtual get-together' and is an website in the Video & Movies category. There are more than 10 alternatives to Zimmer, not only websites but also apps for a variety of platforms, including Google Chrome, Mac, Windows and Linux. The best alternative is StreamParty, which is free. Other great sites and apps similar to Zimmer are Syncplay (Free, Open Source), Watch2Gether (Freemium), Teleparty (Free) and Rave (Free).
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.
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.
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.