It was a real spreadsheet-y day.
We needed to keep track of some inventory for a short time, so the old Lotus-honcho in me stirred, and I whipped up a spreadsheet to act as a database.
Then a little later, I needed to try & work out a sequence of interactions & events, so seeing as the spreadsheet was open, I laid out the concepts on that ... a sort of mind mapping.
That then needed to developed into a graphic which was showing the states of elements turning on & off over time, so ... yup, the spreadsheet.
Of course, that meant that the state diagram which was the next step just *had* to be done on the spreadsheet too. All circles & arrows, and it worked!
That's four uses for a software that started life as a basic accountants tool, without a single $ sign being used.