The number one thing that brought programming to the people was Excel. Multiple orders of magnitude more people have written formulas and macros than have ever used a “real” programming language.
Especially in the days of 65536 rows and 256 columns this was a disaster waiting to happen. And also the 'Can whoever has orders.xls open please close it, URGENT!!' emails. Both issues are now fixed but it's still the wrong tool for the job.
Lotus Notes led to similar horrors.