Alienware Arena offers its members Orcs Must Die Unchained Alpha Key for Windows for free. (Don't have an account? It's free to join. The code will be emailed to you.) Once you have the code, redeem it at the Orcs Must Die website by clicking "My Account" and entering the code. (Don't have an account? Sign-up is free.) The deal will end after 3,000 more key codes have been given out.