Sounds like Christof's ExcelXML class. Recall that I can't use VFP data storage due to > 255 columns.
My class uses the first Excel XML format; the VFPX class uses the current XML format. The old format has the advantage of easily being creatable with text merge, since it's a plain text file. The XLSX Format is a ZIP file with a more complex XML format that requires a library to create files.
Personally, I'm mostly using a commercial product named GemBox these days with Rick Strahl's wwDotNetBridge to call it from VFP.