GNAT or else GNAT Ada is an Ada front-end to the GNU Compiler Collection. GNAT is a validated Ada compiler. It implements all three consequent Ada standards: Ada 83, Ada 95, Ada 2005, and Ada 2012. The front-end itself is written in Ada. GNAT is available for:
Experimental support is also available for:
GNAT is freely distributed under GPL, or with exceptions. There is a version downloadable from AdaCore and another one included as part of GNU/Linux distributions. The License Pragma in source code can be used to help detect packages which use GPL instead of a more permissive license.
For commercial closed-source use, AdaCore also offers GNAT Pro and GNAT High Integrity products. These are basically the GNAT supplied with AdaCore support, and licensed with a special exemption. The exemption prevents proliferation of GPL into the proprietary code compiled by GNAT and linked with its run-time libraries.