Valve's Gabe Newell said: "Steam and Steamworks continues to evolve to keep up with customer and developer demands for new services and content.
"Support for in-game item trading prompted the exchange of over 19 million items. Support for Free to Play (FTP) games, launched in June, has spurred the launch of 18 FTP titles on Steam, with more coming in 2012.
"Looking forward, we are preparing for the launch of the Big Picture UI mode, which will allow gamers to experience Steam on large displays and in more rooms of the house."