Steam sales, you'll undoubtedly have seen the Great Gift Pile giveaway. By completing various game achievements and objectives, Steam users unlock prizes that can be anything from a lump of coal to discount vouchers or even a full copy of any game on Steam. There are reports of people winning massive prizes like Skyrim or the Valve complete pack, and even if you just get a lump of coal, it's still a valuable prize; seven lumps can be exchanged for a new random prize, and those left over at the end of the holiday event will count as tickets in a lottery to win a copy of every single game on Steam.
While many of the achievements require the purchase of cheap indie titles, there are several ways to get your hands on a gift from the great pile absolutely free. Checking your Steam inventory page and trading any item with another user will get you two free gifts, and joining the 2011 Holiday Group will net you a third. Two more prizes can be collected by completing the Son of a Nutcracker! achievement in Spiral Knights and the All I Want for Christmas is Sewers achievement in Rusty Hearts, both of which are free-to-play MMOs available through Steam.
Skip past the cut for details on how to beat the Steam gift achievements for Spiral Knights and Rusty Hearts, including full walkthrough videos.