From their site: 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.
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a very interesting implementation of the spreadsheets API can be found in sisense that created a Provider dedicated to google spreadsheets data and allows you to create amazing dashboards and reports in minutes, it has much more power than the web gadgets.
you can find it in: