Fortran77 has been superseded by Fortran90 and Fortran95. With some extremely minor exceptions, the whole of Fortran77 is a subset of Fortran90, and Fortran95 was a relatively minor revision to Fortran90. Fortran77 is still important because a huge amount of code exists.
GNU's g77 is an excellent Open Source Fortran77 compiler.
There are two incomplete Fortran 90/95 Free/Open Source compilers.
- Convert Fortran 77 to C or C++ (also the name of the GNU Fortran library).
- Fortran 77 program checker.