Yahoo hopes to drive more traffic to its sites by allowing people to share information about their interests and activities with friends. Like on Facebook, they'll be able to create a network of connections and send alerts to those people when they upload photos to Flickr or comment on a story at Yahoo News, for example.

The platform will extend to non-Yahoo sites such as Amazon and Digg, so that users will be able to see from within Yahoo's Web sites what their friends have been doing elsewhere on the Web. And third-party sites will be able to publish user activity back into the Yahoo network, which could help those sites draw more visitors.

The search company is making the data it stores about users -- such as their contacts, interests and location -- available for developers to build their applications. End users will be able to regulate which of their information friends and developers can see, said Yahoo officials, who previewed the platform in San Francisco on Friday.

It's an ambitious project that required Yahoo to "rewire" its properties to create a single underlying platform that connects them all. Those services existed in the past as "silos" that allowed for little interaction between them, said Ash Patel, executive vice president with Yahoo's Audience Product Division.

"The platform is how we start rewiring and reforming the user experience," he said.