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 and Ada 2005. The front-end itself is written in Ada. GNAT is available for:
Experimental support is also available for:
GNAT is freely distributed under GPL.
However, 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.