Guise
It's
Here
http://store.steampowered.com/livingroom/SteamOS/

"Steam is coming to a new operating system
As we’ve been working on bringing Steam to the living room, we’ve come to the conclusion that the
environment best suited to delivering value to customers is an operating system built around Steam itself.
SteamOS combines the rock-solid architecture of Linux with a gaming experience built for the big screen.
It will be available soon as a free stand-alone operating system for living room machines."