ShareTube - Watch YouTube, synced with friends.
Togetherly - Watch Youtube with friends
&chill - Watch YouTube & Twitch videos with people online
Juicebox - Spectacular HTML5 Image Galleries Made Easy
Showgoers - Showgoers is a website dedicated to watching Netflix movies together with friends or loved ones who are not sitting on the same PC.
Random YouTube - A simple website to watch some random YouTube video.