OpenSocial is created by Google. You can build a great, viral social app with little to no serving costs. Instead of hosting your application on your own servers, you can use this service without worrying about your bandwidth demands.

This is a great resource for programmers. FAQ's, Developer's Guide and the Gadget Tutorial, and much more.

Following information is from Google:

http://code.google.com/apis/opensocial/faq.html 

What is OpenSocial?

OpenSocial is a set of common APIs for building social applications across many websites. OpenSocial consists of both JavaScript APIs and Google Data APIs.

 

How does OpenSocial help?

The existence of this single programming model helps both developers and websites. First, developers only have to learn the APIs once in order to build applications that work with any OpenSocial-enabled website. Second, because any website can implement OpenSocial, developers have a broad distribution network to reach users. Websites also benefit by engaging a much larger pool of third party developers than they could without a standard set of APIs.

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