Looking for something to do this weekend? The multiplayer mode for Sledgehammer Games' Call of Duty: Advanced Warfare, the top-selling game so far this year, will be free to play for PC on Steam through Sunday, December 14, at 1 PM Pacific / 4 PM Eastern, Valve has announced.Coinciding with the free play weekend, you can also buy Advanced Warfare for a 25-percent discount through Monday, December 16, at 10 AM Pacific / 1 PM Eastern.