NEW YORK—Friendster, an early online social network that has faded in the United States but remains strong in Asia, has begun letting programmers create photo-sharing applications and other programs that work on Friendster as well as rival sites.

Friendster had already announced support for this initiative, a Google Inc.-led plan called OpenSocial. But this week Friendster released the software tools that let outside programmers easily adapt chats, games and other functions initially made for other online hangouts.

By participating in OpenSocial, now backed as well by Yahoo Inc. and News Corp.’s MySpace, outside programmers can make their applications work on multiple sites with minimal tweaking.

That could, for instance, encourage developers of media-sharing tools for MySpace to adapt their programs for Friendster.

If the programs had to be written from scratch, the effort might not be worthwhile, given Friendster’s smaller audience—1.8 million in the U.S. in July, compared with 39 million for Facebook and 75 million for MySpace, according to comScore.

Likewise, programmers aiming to reach Friendster’s Asian users can easily adapt their tools for MySpace’s audience in the United States and elsewhere.

Friendster’s use in the United States has fallen with the rise of newer online hangouts. Still, Friendster has been hot in Asia, particularly in the Philippines and other markets that the leading U.S. social networks are trying to tap as domestic online advertising growth slows down.

Facebook has yet to publicly back OpenSocial, though Facebook has had tremendous success encouraging developers to write tools specifically for it.

Other participants in OpenSocial include hi5, LinkedIn, Ning, Google’s Orkut and Bebo, which Time Warner Inc.’s AOL recently bought for $850 million.