Mobile Office is an Office suite for the OpenOffice-based OpenDocument format, which allows you to view, edit or create your files on the mobile phone.
As with other office suites, Mobile Office work with text-based documents (.odt files), spreadsheets (.ods) and presentations (.odp).
Mobile Office for S60 2nd edition-based devices is now free (download link). Version for S60 3rd edition costs only 14.99 EUR.