Valve has officially announced that Steam will launch for the Mac OS X operating system tomorrow, May 12th. The company will also subsequently release additional collections of Mac titles that are individually designed to highlight specific functionalities of Steam on the Mac.

The first library of releases on the Mac will demonstrate "Steam Play," which allows players to purchase a game once and then play it on any Steam-compatible computer--this is great news for dual platform households. Gamers who have previously purchased games through Steam will find them available for download in their account.

Portal will be the first game available for the Mac that runs on Valve's Source engine, while Runic Games' action role-playing game Torchlight will also be available the first day of Steam's release. "We're very excited to be bringing Torchlight to the Mac," said Max Schaefer, co-founder of Runic Games. "Having Steam for the Mac solves so many problems for us as a developer. We look forward to our future games coming out on the Mac as well."

Additionally, native OS X support will be available on the Source engine platform, as well as the Steamworks suite of publishing and development tools. The suite will include product key authentication, copy protection, auto-updating, social networking, matchmaking, anti-cheat technology and more.

As of yet, Valve has not announced when it will release its multiplayer first-person shooters--like Team Fortress 2 or Left 4 Dead--on Steam for Mac.

Stay tuned to Maclife.com this week for more Steam news, features and how-tos!