You can play XCOM: Enemy Unknown for free this weekend through Steam.
2K has announced that a free weekend for XCOM: Enemy Unknown is currently active on Steam. The event goes on through 6pm BST on Sunday, September 13.
All you need to do is head over to XCOM's Steam page and download the client. Enemy Unknown and its expansion Enemy Within, as well as all DLC content is also on sale for 75% off. The sale itself ends on Monday, September 14.
XCOM 2 is also available now for pre-purchase. Pre-ordering gets you the Resistance Warrior Pack, which comes with various items you can use to customise your soldiers with and gives you an unlock of one survivor from the old war.