XCOM: Enemy Unknown is free right now on Steam. Play the fantastic reboot to the classic XCOM series for free until Sunday. The deal is part of a 2K Games sale that Steam and Amazon are taking part in this weekend. After Sunday gamers who want to keep Enemy Unknown will have to shell out $10 bucks to retain their progress.

Friaxis Games, developers of Enemy Unknown, is getting ready to launch a massive expansion to with XCOM: Enemy Within featuring tons of new weapons, mechs and new enemies to blow up through the game's "Glam Cam."

Check out some gameplay of Enemy Within here. XCOM: Enemy Within drops for PC, Xbox 360 and PlayStation 3 on November 15.

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[Via Joystiq]