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.ODF File Extension

File Type 1	OpenDocument Formula (Most common)
File Format	File
Common?	No
File Description	Spreadsheet formula used by OpenOffice.org and StarOffice Calc; allows the results of calculations performed within the spreadsheet to be automatically entered into one or more cells; based on the OASIS OpenDocument standard and formatted in XML.
Program(s) that open odf files	Mac: OpenOffice.org Calc Windows: Sun Microsystems Calc (included with StarOffice); OpenOffice.org Calc Unix: Sun Microsystems Calc (included with StarOffice); OpenOffice.org Calc

File Type 2	Open Document File
File Format	Standard File
Common?	No
File Description	Generic file saved in the Open Document Interchange (ODIF) format; may contain several types of Open Document data, saved in the XML-based OASIS Open Document Format; supported by multiple productivity applications.
Program(s) that open odf files	Mac: OpenOffice.org Windows: OpenOffice.org Calc; Sun Microsystems StarOffice Unix: OpenOffice.org Calc; Sun Microsystems StarOffice; odfWeave

Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/odf