Feedly, the web service that inherited a large number of Google Readers users when Google pulled the plug on it, is now offering an API for developers who want to use the Feedly Cloud. You can use the API to access the more than 30 million feeds harvested and indexed by Feedly. The API allows the application to authenticate as a particular Feedly user, or to access everything.
Developers can sign up for the Feedly Cloud Developer Program and gain access to the developer sandbox. Signing up gives you a client id and client secret you can use to authenticate to Feedly. Completed applications can be pointed at the full Feedly data store.