Starbound beta release is looking to be around dec 4th. Assuming arrangements go through with steam.— Tiy (@Tiyuri) November 26, 2013
Barring any unforeseen obstacles from Steam, the Starbound beta should go live within the next couple weeks.
Starbound lead developer Tiy has just Tweeted that the long-awaited beta for the game should go live "around" December 4, provided, of course, "arrangements go through with Steam." The beta will first be open to anyone who contributed to the game's crowdfunding campaign, or anyone who pre-orders the game. While the beta will be handled through Valve's Steam platform, the final full release will also be available as a completely DRM-free download.
Last month, Tiy gave a detailed explanation of exactly how the beta will work. Basically, there will be three stages, each more polished and having more features than the one preceding it. If you have beta access, you can opt-in to the beta at any stage you like.
The December 4 date would seem to refer to the beta's first stage: Progenitor. Progenitor will be a very buggy and unfinished build, and is only recommended for those who "can't wait any longer" and "enjoy giving feedback".
Developer Chucklefish has been updating the Starbound website on an almost daily basis, providing developer commentary on what the team was working on that day. It's a great way to see the game literally develop before your eyes, and it's fantastic to see Chucklefish being so transparent with its work.
Starbound is a 2D pixel-art sandbox-construction game, the spiritual successor to Terraria, which was in turn heavily inspired by Minecraft. "Freedom" is the big word in Starbound, where you can go out in your own spaceship and build bases and collect items all over the galaxy.