Valve has announced SteamOS, a Linux-based operating system built around Steam and "designed for the TV and the living room".

Update #1: the second announce has been made and it's about Steam Machines. A beta is on its way to design and test a box produced by Valve and running SteamOS.

Update #2: the third and last announce is now revealed, it's the Steam Controller, an enhanced and hackable controller. As for the Steam Machines, a beta program has been launched.