The iso_c_binding module provides a portable interoperability between C and fortran programs and libraries. It is available at least in gcc, intel, sun pro and pgi's fortran compilers.
Using this module one can easily write an interface for C function and call it from fortran and vise versa. Without this module developers are left with messy configure scripts or worse guessing what would the naming conventions be.
I know it is part of the 2003 standard and not 95 but it is very useful and may not be too hard to implement.
I hope it is included in open64 soon.