In short
This tool combines several Excel, OpenDocument or CSV files, mixed if need be, to consolidate monthly exports or lists received from several people. When stacking, it puts the rows of the first sheet of each file end to end in a single table, matching the columns by their headers, whatever their order; a “File” column can show where each row came from. When gathering, each sheet of each file becomes a sheet of one workbook. The order of the files is set by dragging and dropping. The result is saved as .xlsx or .ods, or as CSV for a stack. Only values are carried over: formulas and formatting do not follow. The merge happens in your browser.