DataExcel
Open and make Excel files
Turn an .xlsx into a CSV, or a CSV into a real spreadsheet. A spreadsheet is usually the most private file anyone owns — payroll, a customer list, a year of accounts — and this one is read in the tab you are looking at.
.xlsx only. The old .xls from Excel 2003 is a different format entirely and is refused by name rather than failing oddly.
Turn an .xlsx into a CSV, or a CSV into a real Excel file, in this tab. Formulas are not calculated — a cell that holds one shows the result the spreadsheet last saved, and the page says so when there is none to show.