After some not-so-obvious hints, Valve has confirmed that their digital distribution service, Steam, will be coming to the Mac OS X.

Valve's massive list of PC games including Counter-Strike, Left 4 Dead 2, Portal and Team Fortress 2 will be available for Mac users to download and play starting this April.

But if you've already purchased, or will purchase, a title from a Windows machine then that's fine - both versions come in one package.

"Our Steam partners, who are delivering over a thousand games to 25 million Steam clients, are very excited about adding support for the Mac," said Jason Holtman, Director of Business Development at Valve. "We have added a new feature, called Steam Play, which allows customers who purchase the product for the Mac or Windows to play on the other platform free of charge. Steam Play, in combination with the Steam Cloud, allows a gamer playing on their work PC to go home and pick up playing the same game at the same point on their home Mac."

John Cook, Director of Steam Development, added: "Furthermore, Mac and Windows players will be part of the same multiplayer universe, sharing servers, lobbies, and so forth. We fully support a heterogeneous mix of servers and clients."

The cross-platform play is a huge step and something that has only been seen with specific Xbox 360 and Games for Windows titles, most notably Shadowrun, although it didn't settle the endless controller vs. mouse and keyboard argument. Alt vs. command will be up next.

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Kotaku
Steam
Picture: Team Fortress 2's Heavy in iPod form