Tim Moore has recently announced the REST API for WordPress.com, which allows you to access the data available on WordPress.com blogs in many new and fun ways, as well build cool applications on top of the platform, leveraging even the latest “dot com” features, such as likes, follows and reblogs.
You’ll absolutely love the Developer Console, which allows you to run real REST API queries directly from your browser. Tim also mentioned that the API will soon be available for self-hosted WordPress users via Jetpack. For more information check out the WordPress.com Developer blog