Tyler “Ninja” Blevins said goodbye to Twitch today, announcing that he is moving exclusively to the Microsoft-owned streaming platform Mixer. But what, exactly, is Mixer?

It’s not a household name in the same way that Twitch and YouTube are, and its user base is much smaller than the aforementioned sites. Mixer, which was originally called Beam, was acquired by Microsoft in 2016, and it has existed as a potential competitor to Twitch and YouTube Gaming ever since.