pre> https://gcc.gnu.org/wiki/GFortran </pre>
Follow the instructions that come with the package to install gfortran
on your computer.<p> 

<dt><b>GNU C compiler</b>
<dd>An ANSI C compiler is required for compiling Xgremlin. 
If you already have an ANSI C compiler you can use it, otherwise we
recommend that you install the GNU C compiler from the Free Software
Foundation. (GCC is installed by default on computers running Linux and is 
the default xtools compiler on OS X) 

<b>Version 2.6.3 or higher of GCC 