Yahoo and others sign up for Google's new networking venture, though Microsoft and Facebook so far have not.
Yahoo said on Tuesday it is backing a program by rival Google to make software work fluidly across different social networks, and will create a joint foundation to promote the effort.
The normally fierce competitors are working together in the OpenSocial network, which Google formed in November to lure Web software developers and other social network sites away from the emerging market leader in social networks, Facebook.
Many social networks -- including News Corp's MySpace, Friendster and LinkedIn -- support OpenSocial, a set of technical specifications that lets software developers build applications such as games and photo shows that can run on any social network, expanding the audience for such software.
However, neither Facebook nor Microsoft, which gave Facebook $240 million in backing last year, has signed up to support OpenSocial. Microsoft, which has mounted a $42 billion hostile takeover bid for Yahoo, also has an agreement to sell advertising on Facebook's site.
One industry analyst says OpenSocial is in catch-up mode.
"There is only one place developers go right now, and that is Facebook," Forrester Research analyst Charlene Li said.
"OpenSocial makes it easier for everybody else to get in the game," said Li.
The scope of OpenSocial is increasing and OpenSocial applications reach more than 200 million users, Joe Kraus, a Google director of product management, said in a conference call. Supporter MySpace alone counts 110 million active users.
"If you want to go fast, go alone, if you want to go far, go together," Kraus said of the OpenSocial effort, which is currently endorsed by more than 15 companies.
Kraus founded JotSpot, a maker of software for building small group Web sites, which Google acquired last year.
Yahoo, Google and MySpace also said on Tuesday they will create the OpenSocial Foundation to maintain a neutral, community-governed forum for developing applications. It will be set up as a nonprofit entity, with assets to be assigned to the new organization by July 1.
In a show of Yahoo's willingness to work with Google, a potential ally in its attempt to fend off Microsoft's unsolicited takeover bid, Yahoo vice president of platforms Wade Chambers took the unprecedented step of posting the news on an official Google corporate blog aimed at developers.
"Openness is in the Internet's DNA and it's also a major aspect of our culture here at Yahoo," Chambers posted on the Google blog at tinyurl.com/yoldy3/.
He declined, on the joint conference call, to give specific examples of how Yahoo plans to use OpenSocial applications.
Yahoo executives have showcased new versions of their flagship e-mail service, Yahoo Mail, and software for using the Internet on mobile phones that have deeply integrated social network features. A key stated goal of Yahoo is to become a primary starting point for Web users not just to reach Yahoo's own media properties but also other social networks and sites.
Facebook, which has had the greatest momentum among social networks in attracting new users over the past year, has remained aloof from OpenSocial. It offers its own simple set of technical specifications for application developers.
Independent developers have built 19,000 applications that run inside Facebook, which now has 67 million active users.
Yahoo's Chambers said it would welcome Microsoft or any other company that wants to sign on.
"Any large player should be open to participate," he said.