https://www.pcgamer.com/what-happened-to-steam-machines/

In light of Valve removing a link to Steam Machines from the front page of Steam, we've republished this article, originally written in July 2017. 

On September 23rd, 2013, Valve announced SteamOS: A Linux-based operating system just for PC gaming. Two days later, it hit us with another surprise: Steam Machines, a line of pre-built PCs from multiple manufacturers that would sit under our TVs like consoles and run this new OS. Forget PlayStations and Xboxes and especially Windows 8, which Valve boss Gabe Newell called “a catastrophe for everyone in the PC space.” Valve was going to invade the living room with an open-source island that Microsoft couldn’t control.