I've worked on a project that was intended to replace Excel spreadsheets with a web front end. It was presented like we were moving our processes out of the stone age - as if we were replacing a pen-and-paper process that "doesn't scale", or whatever.

I will never do that again. We didn't build a whole spreadsheet engine, but we did build a web UI that simply doesn't do as much as Excel. Excel is powerful. Sometimes it's a fine tool for the job. Our team was laid off before we could roll it out, but I remember the growing sinking feeling of "I would hate using this if I already had a bunch of habits built up in Excel"