It is not "Fortran 77 only" but supports the F77 standard perfectly, is actively maintained, runs natively on 64-bit Windows, and is completely free.
Fortran 77 may be decades old, but it still powers scientific computing, engineering simulations, and legacy financial models. If you have old .f or .for files and need a reliable , you don’t need to pay for expensive commercial software. fortran 77 compiler for windows 10 64-bit free download
