Mixer (formerly Beam) is a streaming service that Microsoft acquired in mid-2016. Like Twitch, Mixer allows gamers to stream their gameplay while interacting with viewers via a text-based chat interface. The difference between Mixer and Twitch, primarily, is the remarkably low latency Mixer has between the streamer and the chat pane.
Mixer also has an SDK which allows developers to bake remote controls into their games allowing viewers to interact directly with the streamer's play, should the streamer enable it. The service is also integrated into the Xbox One OS and Windows 10, adding another social pillar to Xbox Live's increasingly diverse network.