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

1️⃣ Programs are column sensitive

2️⃣ DO loops

3️⃣ No WHILE loop

4️⃣ DOUBLE PRECISION variables

5️⃣ Output with FORMAT