FreeDOS includes a FORTRAN 77 compiler as the Open Watcom FORTRAN compiler.
If you're interested in trying out FORTRAN, here are a few points to get you started:
https://www.both.org/?p=14100
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@nprofile1q... Ooo! Ooo! Don't forget the three condition if statements! That's pretty rare anywhere else, but it's core Fortran.