Steam

From SingularityShift

Steam is a digital distribution, management, and community platform for PC games developed and maintained by Valve Software.

Since it's opening, it has acquired an active user base of over 15 million gamers, and many publishers have signed on to build a collection of hundreds of titles and videos for direct download.

Visit the Steam homepage for more information or to download the client.

Note that SteamLab can download, install, and manage Steam automatically for you.