Social Graph API
= makes information about the public connections between people on the Web easily available and useful
URL = http://code.google.com/apis/socialgraph/
Description
"makes information about the public connections between people on the Web easily available and useful. You can make it easy for users to bring their existing social connections into a new website and as a result, users will spend less time rebuilding their social networks and more time giving your app the love it deserves.
Here's how it works: we crawl the Web to find publicly declared relationships between people's accounts, just like Google crawls the Web for links between pages. But instead of returning links to HTML documents, the API returns JSON data structures representing the social relationships we discovered from all the XFN and FOAF. When a user signs up for your app, you can use the API to remind them who they've said they're friends with on other sites and ask them if they want to be friends on your new site." (http://google-code-updates.blogspot.com/2008/02/urls-are-people-too.html)