OpenSocial defines a common API for social applications across multiple websites. With standard JavaScript and HTML, developers can create apps that access a social network's friends and update feeds.
A common API means you have less to learn to build for multiple websites. OpenSocial is currently being developed by a broad set of members of the web community. The ultimate goal is for any social website to be able to implement the API and host 3rd party social applications. There are many websites implementing OpenSocial, including Engage.com, Friendster, hi5, Hyves, imeem, LinkedIn, MySpace, Ning, Oracle, orkut, Plaxo, Salesforce.com, Six Apart, Tianji, Viadeo, and XING.

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