500x_custom_1273588505706_steamengine.jpgValve's dominant games-downloading service Steam comes to Macs tomorrow, bringing with it Diablo-style indie hit Torchlight and Valve's very own first-person puzzle hit Portal.

If you bought Portal or Torchlight via Steam on your Windows-based PC then you may in fact already be the proud owner of tomorrow's releases. Portal (and possibly Torchlight — the press release is unclear) will support a feature called Steam Play, which, according to a press release from Valve today, "allows customers to purchase a game once and play it on all Steam supported platforms. Gamers who have previously purchased games on Steam will find them available in their account on the Mac as they are released."

Steam on Mac will launch new games each Wednesday, according to a Valve. The company's news today only mentions Portal and Torchlight for May 12. We're checking with Valve to find out which other games, if any, will be out through the service tomorrow.

While you await Steam's Apple debut, you can watch video of the program in action.

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