Late last week Google quietly announced their Google Spreadsheets API, the latest in their GData family of APIs. What does it allow you to do? From their announcement: "The Google Spreadsheets data API allows client applications to view and update Spreadsheets content in the form of a Google data API ("GData") feeds. Your client application can request a list of a user's spreadsheets, edit or delete content in an existing Spreadsheets worksheet, and query the content in an existing Spreadsheets worksheet. " Creating new spreadsheets and deleting existing ones is not supported in this initial release.
You can see a summary of the API in the new entry at ProgrammableWeb.
GData, Google's extension of RSS 2.0 and Atom 1.0, is now used for a variety of Google APIs: