Open Document Format aka ISO/IEC 26300
ISO/IEC 26300, Open Document Format for Office Applications (OpenDocument) v1.0
has been designed to be used as a default file format for office applications with no increase in file size or loss of data integrity.
It will allow users to save and exchange editable office documents such as text documents (including memos, reports, and books), spreadsheets, databases, charts, and presentations – regardless of application or platform in which the files were created.
http://www.iso.org/iso/en/commcentre/pressreleases/2006/Ref1004.html
OpenOffice.org uses ODF !