GNAT is the GCC Ada compiler. As such, it is required to compile GHDL- which is the reason why it is hosted here.
For all general-purpose applications, you should use one of the properly maintained package from other sites:
The package has been created from the source code provided on macada.org. The main difference is, that the package provided here installs to /Developer/Ada. This makes sure that there is *really* no conflicts with an existing Xcode install.
To download the GNAT installer, go to the SourceForge project page:
The GNU Public License is the key to free software. To learn more about the goals and licenses of the Free Software Foundation see here: