updated 07:45 pm EDT, Wed May 15, 2013
Beta in progress, users can sign up for future invitation
Digital game marketplace Steam has added a new feature -- in-game Steam Trading Cards. Steam Trading Cards are virtual cards earned by playing games on Steam. Sets of cards can be turned into game badges and tradable Steam community items, including discounts on titles or downloadable content, profile graphics, and custom game-related emoticons.
Cards are collected though play of any of the Trading Cards beta games, such as Team Fortress 2, DOTA 2, Portal 2, Half-Life 2, and Don't Starve. Half of a card "set" is dropped during the course of regular play, and the rest are obtainable through gameplay similar to achievement earning or by trading with other users.
Once a set of cards is collected, users can craft them into a game badge. The new badges earn tradeable virtual items for Steam users, which are summarized for the user and the community and can be advanced with game play, earning non-tradeable items like profile showcases, extra friends list slots, and other benefits.
The "cards" are not currently usable outside of the trading mechanic, but a Steam FAQ page lists that they are looking into the possibility. Titles will have card trading functionality added "slowly" over the next few months.