I looked this up. Haven't played it yet, but here's a quick video:
Their website: https://warframe.com/
Site currently giving away free beta keys: Exclusive Warframe Betakey Giveaway! | MiscGaming.org
As of right now there are about 2660 keys left. (5:15pm EST 2/01/13)
Edit: I couldn't get IE9 to display the beta key, had to open up Mozilla to see it on Miscgaming.org's website. Just an FYI if you have issues.