Team Fortress 2 is following in the footsteps of agricultural Facebook games, time-sink iPhone apps, failed MMOs and Korean kart racers. Valve’s comedic class-based shooter has gone free-to-play on PC and Mac.

Valve, the game’s developer and maker of Half Life and Portal, will only earn money from the shooter’s wildly popular virtual haberdashery of in-game hats and digital arsenal of upgraded guns. The vast majority of that content can also be earned for free through playing the game.

Valve’s Team Fortress lead Robin Walker assured Develop Online that nonpaying gamers will not be subjected to advertising, there will be no premium subscription models and having a massive wallet won’t automatically let you buy the best weapons and trounce the competition.

He also explained that item freebies, which are currently doled out regularly, will still be made available to nonpaying gamers, and at the same frequency.

Valve introduced microtransactions (aka, the ability to spend a few bob on in-game items) in October 2010 with the Mann-conomy update.

Instead of slogging through endless battles to earn or randomly find new weapons, players can buy them from the shop with real-world currency. You can also buy endless numbers of hats like deer antlers, a luchador mask or a plunger for your noggin.

Valve doesn’t release sales data, but given the fact that it’s resting the entirety of Team Fortress 2’s profits on digital headwear, we can assume they’ve sold quite well so far.

Team Fortress 2 has also been updated with a more newbie-friendly training mode and match-finder, as well as another Payload map, the “Uber Update” (new weapons for the Medic) and the gruesome CGI short Meet the Medic, which you can watch above.