Put on your boot partitions—the SteamOS beta has released to the public alongside the initiation of its beta program, which will put 300 prototype Steam Machines into the wild. For the estimated 7,129,999,700 of us not selected for that program, a living room machine running the new, free, Linux-based OS is still doable, though installing it may require some tinkering—Valve suggests you wait until 2014 unless you're an "intrepid Linux hacker." Challenge accepted .
At the time of writing, Valve has not officially announced that SteamOS 1.0 "Alchemist" is available for download. We expect a page to go live at store.steampowered.com/steamos/beta/ later today. [Update: it's live.] Steam Universe group officer Jvert (presumably Valve engineer John Vert), however, has confirmed that the correct download link is at repo.steampowered.com/download/ .
Unfortunately, that download will most likely fail right now. To help spread the data, Steamdb has created an unofficial torrent , but use caution when downloading from any unofficial source. [Update: Valve has provided MD5 and SHA512 checksums to verify that your download is genuine.] You can find system requirements and installation instructions in the official FAQ —note that AMD graphics cards are not currently supported.
SteamOS is meant to free Steam's game library from the desktop, extending Valve's domain to the living room with a superior couch-based PC experience and some of the features that have become standard on consoles, such as media streaming services. For Valve, it's also about declaring freedom from Microsoft—SteamOS will only run games with Linux support (of which we expect to see many more in the coming year). That bold statement is tempered by the ability to stream games from a Windows PC to SteamOS over a local area network, though how much it's tempered will depend on how well streaming works.
We'll be playing with SteamOS this weekend, and plan to have impressions and installation tips for you as soon as possible. If you're the patient type, Valve's Steam Controller and third-party Steam Machines will be available until next year, no "Linux hacking" required, presumably.