Valve Developing a New Free-to-Play Project
Valve has been constantly updating their Steam digital download platform ever since it's inception in 2004. One of the more recent updates for the service was the Steam "wallet", allowing users to add money to their Steam profile so that later transactions would be easier and faster. This made micro-transactions for items in Team Fortress 2 quite easy, but it also fits quite well with a recent rumor that Valve is currently developing a free-to-play project.
The information that Valve is creating a micro-transaction heavy title comes from Barre De Vie, a French-language based gaming website. According to the site, Valve's head of marketing Douglas Lombardi replied "yes" to the question of if the studio was developing it's own free-to-play, micro-transaction title. Lombardi apparently offered no other information about the unknown title, and has since not replied to any requests for comment.
There are a few possibilities here. One is that Valve has just started developing a free-to-play multiplayer title amidst the rapid succession of free-to-play games (Battlefield, Ghost Recon), though that doesn't sound like something Valve would do, as they are rarely reactionary in their development. The free-to-play project may be something we've already heard of, too, like Defense of the Ancients 2, the official sequel to the popular Warcraft III mod. It could also be an unannounced sequel of a popular Valve multiplayer game, such as Counter-Strike, Left 4 Dead or Day of Defeat. As with all rumors, any of this could all be false, but that's unlikely with the Steam wallet and Valve's recent Team Fortress 2updates.