Google has released an API for their Spreadsheets program. You can use it to get a list of spreadsheets for an account, to add or delete rows from a spreadsheets or to send simple SQL-like queries.
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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Google Spreadsheets API, Google Spreadsheets