SAN FRANCISCO: Zynga Inc., the biggest maker of Facebook games, began letting users of Microsoft Corp.’s games site play its most popular application, “FarmVille.”

The agreement is “the first step towards bringing Zynga’s social games to Microsoft’s platform,” the San Francisco-based company said today in an e-mailed statement. Additional titles will be introduced on Microsoft’s MSN Games and Windows Live Messenger service in the coming months, Zynga said.

Zynga, founded by Mark Pincus in 2007, has relied on Facebook Inc.’s dominance in social networking to draw millions of users to its games. “FarmVille” is the top game on the site, with 76 million users a month, according to research firm Inside Network. Zynga, which makes money by letting players buy virtual goods, aims to build on its popularity by expanding to other sites.

MSN Games, a unit of Redmond, Washington-based Microsoft, has more than 1,000 games that can be played through a Web browser, including “Bejeweled,” “Mah Jong Tiles” and “Spades.” The service competes with services from Yahoo! Inc. and AOL Inc.

Games on Facebook and other social networks gained popularity in the US last year, prompting Electronic Arts Inc. to purchase Playfish Inc., the maker of “Pet Society” and “Restaurant City,” for $400 million. Zynga raised $180 million in private capital in December from Digital Sky Technologies, a Russian investor in Facebook.

Facebook Connect

Zynga also runs the No. 2 game on Facebook, “Café World.” In total, the company has more than 230 million monthly users on Facebook, according to Inside Network. MSN Games users will play “FarmVille” through Facebook Connect, a service that links Web sites.

In 2007, Microsoft paid $240 million for a stake in Facebook, which at the time valued the Palo Alto, California- based company at $15 billion.

Microsoft dropped 79 cents to $27.84 at 4 p.m. New York time in Nasdaq Stock Market trading. The shares climbed 57% last year.