Valve officially revealed Monday that its Steam online gaming service, along with the Source engine that powers titles such as Half-Life 2 and Left 4 Dead 2, is coming to the Mac in April. Valve's library of games will be making the jump from Windows Machines, including Team Fortress 2, Counter-Strike, Portal, and the Half-Life series. "As we transition from entertainment as a product to entertainment as a service, customers and developers need open, high-quality Internet clients," said Gabe Newell, president of Valve. "The Mac is a great platform for entertainment services." Jason Holtman, director of business development at Valve, said the ...