Announced yesterday in the first of three promised major announcements, SteamOS is a Linux based OS that is built specifically for TVs and the living room, but available for all computers. While the OS is unsurprisingly game focused, it will also incorporate music, TV, and movie services, fitting in with the goal of being a living room OS.
Other important details: the announcement page makes repeated mention of how easy it will be to stream with the OS makes note of how a SteamOS machine will be the device used to connect TVs with desktops. The Steam box has project has been public knowledge for a while know, but it seems to be that it may come as one of the announcements this week. On top of it all, the SteamOS will be free to download and free to license to manufacturers, meaning gaming PC builders will be able to stock the SteamOS as a standard.