The Humble Monthly subscription plan delivers you a selection of new games (to keep!) every month, gives you 10% off everything in the Humble Store, and donates 5% of each month’s proceeds to charity, but if all that wasn’t enough to get you to sign up, how about a free copy of X-COM UFO Defense?
Source: Kotaku – For 48-Hours Only, Humble is Giving Away X-COM UFO Defense for Free