Excuse my english.
I create an html file, tables and embedded css, and save it with the xls extension. Even with formulas.
Office 2000+, OpenOffice and Gnumeric can open this files very well.
You can go further connecting your xls file with a cgi app in a web server. I do this to dinamically fill cells in Excel with "Web queries". OpenOffice supports this too with more flexibles options.
Freepascal rules ! I can use my xls units in console apps, cgi apps and Lazarus apps.
Gustavo
