Simply Fortran runs great under WINE on GNU/Linux and *BSDs.  I use it daily myself.  Make sure first that WINE is installed, then just download the Simply Fortran installer and run it.  There are a handful of users that I know of using it on Linux exclusively.

The only point to note is that Simply Fortran will continue to build Windows executables.  It will not be using the native Fortran compiler. Also, I have some problems on occasion with the Start panel under Linux; it doesn't seem to populate entirely due to a missing feature in WINE.  Other than that, it does run fine.

Recalling (IIRR) that Simply Fortran runs under CygWin, does that mean, by any chance, that you might one day be able to make it run in a Linux environment?

I'm nearly sure that this is a daft question, but that's never stopped me from asking them before!
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John