SteamOS to be Released on Friday the 13th
Get an early taste of SteamOS.
While it must be disappointing news for those internationally that the 300 Steam Machine beta boxes will be confined to the U.S. only, it's not all bad. Friday the 13th will bring some good fortunes to those who want to take the SteamOS software for a spin, as Valve will make it downloadable tomorrow.
Valve does caution that the SteamOS release tomorrow is meant for those who know their way around Linux, so anyone else may want to hold off until January. After all, it's not like you can't run all your Steam library from Windows.
"SteamOS will be made available when the prototype hardware ships," Valve wrote. "It will be downloadable by individual users and commercial OEMs. (But unless you’re an intrepid Linux hacker already, we’re going to recommend that you wait until later in 2014 to try it out.) We’ll post info soon about that. Oh, and stay tuned for the in-home streaming beta to begin soon, too!"
Here's a photo from the production line. We're already jealous of those lucky 300.
So far we've seen two other Steam Machines:

Yes, but no word on whether streaming or anything is included. Most likely not. That being said, I am cleaning an old laptop for installation as I am typing this.
Nope, it's a OS not a system package. Unless it's an Ubuntu derivative, in which case is something along the lines of "sudo apt-add-repository ppa:steam/SteamOS" and then "sudo apt-get update".
Sorry, couldn't help my linux e-peen.
i would expect any game with linux support will work. i will be installing for sure on my htpc (dual boot with windows). something that tickles my fancy is the game streaming from another pc, so i can have my low end htpc hooked up to my tv and still run demanding/windows games via streaming from my main pc on the big tv screen.
Neither have I.....
(yeah, my luck ain't that good.)
http://repo.steampowered.com/download/
What do you need to run SteamOS? Here's the hardware list from the FAQ:
Intel or AMD 64-bit capable processor
4GB or more memory
500GB or larger disk
NVIDIA graphics card (AMD and Intel graphics support coming soon)
UEFI boot support
USB port for installation
Note: one of the installation methods that Valve details requires a 1TB storage device.