As expected, Microsoft launched an assault on Steam and other similar services by opening up its Games for Windows Live Games on Demand digital distribution feature late yesterday. As the name suggests, Games on Demand will allow users to purchase titles, using a credit card or by redeeming Microsoft Points, and download them directly from their PC. For now, however, the service's catalog is limited to just 13 games.

As part of an introductory offer Microsoft is giving 50 percent discounts on Shadowrun, a decent online shooter that never got much attention, and life simulator Viva PiƱata. A free copy of puzzle game Tinker, which had previously been released with Windows Vista Ultimate, is also available for download.

Besides these titles the rest of the lineup includes Fallout 3, DiRT 2, Resident Evil 5, Street Fighter IV, Battlestations Pacific, FUEL, Kane & Lynch: Dead Men, Section 8, Juiced 2, and Red Faction: Guerrilla. Previously promised indie titles Osmos and World of Goo are strangely absent from the list, however.

Prices are comparable to other digital distribution services, ranging from $9.99 to $49.99. If you are new to Games for Windows Live you can download the client here, while existing users will need to update to the latest version (v3.2) in order to access the Games on Demand feature.