Steam is a digital distribution and communications platform developed by Valve Corporation. It is used to distribute a large number of games and related media entirely over the internet.
Valve announced that Steam is coming to the Mac in April along with the Source engine to bring you games like Team Fortress 2, Counter-Strike, Portal, and the Half-Life series.
"Our Steam partners, who are delivering over a thousand games to 25 million Steam clients, are very excited about adding support for the Mac"
Mac and Windows players will be part of the same multi-player universe, sharing servers, lobbies, and more.
Then there is 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.