Valve's newest community focused feature, Steam Trading Cards, has opened its beta. Trading Cards, which allows players to earn game-specific trading cards that can then be used to procure badges, profile backgrounds, store coupons and more, currently has support from 6 games - Counter Strike: Global Offensive, Team Fortress 2, Portal 2, Dota 2, Half Life 2, and Don't Starve - with more coming as Valve gets them done (must resist HL3 joke.....)

You can get more information about the system at Steam's info page, or sign up for the beta on the group page.