Google's OpenSocial got a major boost on Thursday when MySpace, the world's most popular social networking site, announced it will participate in the project to streamline the creation and adoption of social Web applications.

This means that MySpace, like other OpenSocial participants, will be able to offer all applications created by third-party developers that are compatible with the OpenSocial application programming interface (API).

For developers, the addition of MySpace to OpenSocial is a major step, opening their applications to that social networking site's massive base of users.

On Tuesday, Google confirmed the existence of the OpenSocial program, which is widely seen as not only Google's strongest move in social networking to date, but also as a response to the rising popularity—and threat—of Facebook.

Although Facebook is the second-most popular social networking site in the world, it is growing faster than MySpace, thanks in large part to the fact that Facebook opened its platform to external developers in May, something MySpace is only now about to do.

To date, Facebook has about 7,000 applications available for its members. It hasn't said whether it will participate in OpenSocial, although Google says the door is open.

"Despite reports, Facebook has still not been briefed on OpenSocial. When we have had a chance to understand the technology, then Facebook will evaluate participation," Brandee Barker, Facebook spokeswoman, said in an e-mail.

OpenSocial can, in theory, dilute this distinguishing feature of Facebook, by offering a core set of APIs that will let developers write an application once that is compatible with multiple sites.

In other words, OpenSocial seeks to address the inconvenience for developers of having to port applications to different social networking Web sites.

In addition to MySpace, other partners participating in OpenSocial include Oracle, Salesforce.com, Hi5, iLike, LinkedIn, Slide, Ning, Friendster, Six Apart and Plaxo.

The recent furor over Facebook, MySpace and Google's OpenSocial is indicative of the rising importance of social networking sites for people both in life and at work.

Originally considered of interest only to teens and young adults for communicating with friends, these sites have broadened their demographic appeal as they have proven useful for more activities, including professional networking and business activities.

For Google, which has had the Orkut social networking site for several years, its reaction to this revolution is belated, but the company recognizes that it needs to improve its position in this space.

Within sites like Facebook, a lot of formerly dispersed online activities are united under a single virtual roof, making these sites very attractive for advertisers. That's because people share a lot of personal information about themselves on the sites, making the users easy to target with commercial pitches.