Play for free, and then pick them up on the cheap
The latest free weekend events have begun on Steam, and this time around they include the latest XCOM and a pair of Saints Row games.

Beginning now and running until Sunday, September 13, at 10 AM PDT, you can play XCOM: Enemy Unknown, Saints Row: The Third, and Saints Row IV for free as much as you want. As always with these Steam events, you have unlimited access to the games as long as they are available, letting you play to your heart's content.
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XCOM is also on sale for $7.49, as is its Enemy Within expansion. Other DLC packs are available for just a few bucks, or you can buy the Complete Pack (with the base game, Enemy Within, and the other DLC) for just $10--an especially good deal. Meanwhile, upcoming sequel XCOM 2 is now available for preorder on Steam.

Should you decide to purchase any of the free games, you'll be able to carry over your progress.

You can download the free games through their Steam pages, each of which is listed below:

Saints Row: The Third (PC)
Saints Row IV (PC)
XCOM: Enemy Unknown (PC/Mac/Linux/SteamOS)