The Community team at Robot is Generous enough to give the Alpha players a few Keys every now and then to give away during Twitch streams or to friends. A few of them are using Reddit to get them out to people who haven't received an Official invite yet.
http://www.reddit.com/r/pcmasterrace/comments/2tjeje/orcs_must_die_unchained_beta_giveaway/
Orcs Must Die! Unchained is in closed beta and you can read more and sign up at OrcsMustDie.com
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