On the Zend Developer Zone today, there's a new post from Maarten Balliauw about a set of PHP classes he's created to work with Office 2007 SpreadsheetML documents (yay! another format!).
I finished my first goals (some basic XLSX writing), and I want to share this set of classes to the community. [...] Each cell supports the following data formats: string, number, formula, boolean. Visual formatting is not implemented, but I'll get to that later.
Features supported currently include the creation of the Spreadsheet object, adding worksheets, adding cells, and exporting the object to the Excel 2007 OpenXML format.
You can check out the project and the latest version over on his blog.