ShareTube - Watch YouTube, synced with friends.
Parallel - Listen to music with friends over Spotify at the same time
Showgoers - Showgoers is a website dedicated to watching Netflix movies together with friends or loved ones who are not sitting on the same PC.
Slackbox - Spotify playlist collaboration through Slack
Netflix Party - Netflix Party is an extension for watching Netflix remotely with friends and family for movies nights with that long-distance special someone.
Join My Playlist - Listen to music live together with your friends in Spotify.