Everytime I mention Fortran there is an uptick in the site views so I know there are plenty of readers with an interest in Fortran on a Mac.
There is an interesting post on the NextMove Software blog, Just what you wanted for Christmas – a compiler for Gaussian.
This package provides a “pgf77” script that emulates the Portland Group’s PGI fortran 77 compiler, instead using the Free Software Foundation’s GNU gfortran compiler instead. This emulation is sufficient to allow packages such as Gaussian03, that would otherwise require a commercial compiler, to be built using open source tools. In addition, this package also allows Gaussian03 to be built on a case-insensitive file system (such as when using Mac OS X, cygwin or a FAT32 drive) by overriding the behaviour of “cp” and “gau-cpp” such that they don’t cause problems when used by Gaussian’s build scripts on non case-sensitive file systems.
gXXforrtran is available on GitHub In theory, it should work for a standard Linux or Mac system.
However, as they don’t have access to the Gaussian source code they can't check it. Anyone out there care to try it?
See also Fortran on a Mac page