Apple TV - New Apple TV running tvOS
Watch2Gether - Watch2Gether is an app that allows multiple people to watch the same content simultaneously and interact with each other while watching.
NVIDIA Shield TV - Streaming box with Google Assistant and Google Cast.
Metastream - Watch streaming media with friends
Mi Box - 4K Ultra HD streaming and gaming box powered by Android TV
StreamParty - StreamParty is a watch communiry, that allows you to watch video streams in sync with the people you care about, on multiple services.