... and what's wrong with Access (I presume you meant), FoxPro or dBASE? What else would they be coded in?
Take a close look at HECS (.dbf data files), for example.
Notice too that I did say "foundation" and "original code"!
Just for the record, I know of a commercial system that was coded in C (but that would have been at least twenty years ago now). And, in case anyone is wondering (?) I also knew the coder (not me, I hasten to add).
OK (and just to forestall the argument) ... here's the challenge:- anyone who has these "industry standard" programs (and who also has the nous
to be able to do it), take a look at the file types (or failing that, the data files) and let us know their findings! That is, see if you can work out what language the program was coded in, and/or which format do the data files follow?
And, of course, if anyone has access to the source
code (which I very much doubt ... and therein lies the rub) ... well, then we could know for sure!