Mega developer Valve has launched a public beta for online shooter Team Fortress 2 over three years after its release.

Why? To test "new technologies without the risk of breaking the game", the developer wrote on the Team Fortress 2 blog.

Valve's testing class, item and weapon changes. Mysterious "higher level, game-wide experiments" are going on, too.

And as with all betas, the developer wants your feedback.

"As you've probably seen by now, we like to change things in Team Fortress 2," Valve said. "A lot. And while we're perfect most of the time, we occasionally get something wrong. One reason for this is we just don't get enough data from internal play testing, and another is that we spend too much time watching Tom Bui serenades on YouTube."

The beta is open to all who own the game. To install, launch Steam, open the Library and install "Team Fortress 2 Beta" from your games list.

Tom turned up a 9/10 in Eurogamer's 2007 Team Fortress 2 review. The game was bundled with Portal, Half-Life 2, Episode One and Episode Two in stunning compilation The Orange Box.

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Team Fortress 2 players beware! The game's first AI boss beheading your way, clippity-clop, clippity-clop.

He's the Horseless Headless Horsemann, a long lost Mann family member, and he appears randomly on spooky Halloween map Mann Manor. And he wants to kill you - providing the Manor's exploding pumpkins don't get you first.

Those brave enough can face the Horseless Headless Horsemann in battle. Slay him and an achievement awaits. It's called "Sleepy Holl0WND".

In addition to Triple-H (as I'm calling him), the Team Fortress 2 Halloween celebrations offer loads of themed costumes and items. You can buy them at the Mann Co. Store, and many will will be made by the community - we've already heard of the riches that can be earned by creative and enterprising fans there.

In two weeks five modders from the Team Fortress 2 community made between $39,000 and $47,000 selling items through the game's new Mann Co. Store.

The royalty figures were so high they exceeded PayPal deposit restrictions, so Valve flew the highest earners - Spencer Kern and Steven Skidmore - to its door to hand the cheques over in person.

"It was completely mind-blowing, the size of the return that we're getting on these things," Kern gushed to Gamasutra.

The Mann Co. Store was added to Team Fortress 2 (PC) at the very end of September. It enables player-to-player trading and provides a storefront for modders to sell their TF2 content. Creators keep 25 per cent of the money made.

"It benefits us because it grows the community, right? These [content creators] benefit, but we benefit too," reasoned Valve brain Gabe Newell.

"Team Fortress 2 is a better product because we have community contributions in it. They're going to go off and listen to what the community says about how they can do that better, and we can draft along, as we both benefit."

Newell reckons the idea will eventually catch on: "Once people ... realise this is about their community, and that the right people are getting the benefits, ... after a while, they'll say, 'This is really how these kinds of communities need to work.'"

Team Fortress 2, a caricature-styled multiplayer shooter, was released to wide acclaim in the autumn of 2007. Three years on, the PC TF2 community is as healthy and enthusiastic as it ever was, thanks to devoted support from Valve. The same isn't true of the PS3 and Xbox 360 versions of the game, as the closed nature of Xbox Live and PlayStation Network has made it impossible for Valve to unleash the same amount of downloadable support.

Tom Bramwell reviewed Team Fortress 2 for Eurogamer.

Video: The characters of Team Fortress 2.