Oh absolutely. Don't forget about the giant mess Microsoft made in countries like the Netherlands, where Excel will refuse to automatically open comma-separated

Oh absolutely. Don't forget about the giant mess Microsoft made in countries like the Netherlands, where Excel will refuse to automatically open comma-separated values files (you know, CSV), unless the separator is a semicolon — because someone in the past thought that was how the Dutch did it. You want people to be able to open your nice and sensible CSV files in Excel? First figure out which arcane locale specific settings you need, then generate those monstrosities and annoy anyone who genuinely expected Unicode comma-separated values. My solution was to just write a generic spreadsheet writer component in our API and have it generate CSV (normal, comma-separated, UTF-8), XLSX, or ODS. Anyone using Excel just grabs the XLSX output. Generating XLSX and ODS was just a matter of saving a minimal example file for each and figuring out where to write cells and rows. No extra library needed (both file formats are just zipped up XML files), and everybody is happy.