GNAT GPL edition refers to the versions of the GNAT Ada compiler licensed under the GNU Public License (GPL). Prior to 2005 GNAT was distributed under so-called GNAT-modified GPL license (GM GPL), which allowed the code compiled with GNAT and linked to its run-time library to be used commercially. All newer public releases of GNAT distributed by AdaCore are licensed under strict GPL. AdaCore continues to distribute GNAT under GM GPL, sold as a part of its commercial product GNAT Pro.
GNAT GPL is part of GNU Compiler Collection. You may find other members of GNU Compiler Collection at Category:GNU Compiler Collection.