OpenSocial. It is "a set of APIs that allow developers to connect with social sites."
From Google site (here):
"The web is fundamentally better when it's social, and we're only just starting to see what's possible when you bring social information into different contexts on the web," said Jeff Huber, senior vice president of engineering, Google. "There's a lot of innovation that will be spurred simply by creating a standard way for developers to run social applications in more places. With the input and iteration of the community, we hope OpenSocial will become a standard set of technologies for making the web social."
One of the most important benefits of OpenSocial is the vast distribution network that developers will have for their applications. The sites that have already committed to supporting OpenSocial -- Bebo, Engage.com, Friendster, hi5, Hyves, imeem, LinkedIn, mixi, MySpace, Ning, Oracle, orkut, Plaxo, Salesforce.com, Six Apart, Tianji, Viadeo, and XING -- represent an audience of about 200 million users globally. Critical for time- and resource-strapped developers is being able to "learn once, write anywhere" -- learn the OpenSocial APIs once and then build applications that work with any OpenSocial-enabled websites.
Also see an hr long camp side video here.
My take: Classic standard setting effort. May actually work as it will make all social sites more powerful from the users point of view. Lots of players have joined. But what will Facebook/ Microsoft say?