The GATK package download includes all released GATK tools. Please see Getting Started for a quick start primer on using GATK, and see the Version History for release notes and highlights of differences between versions. You will need to be registered and logged into the GATK forum to access the download.
All POSIX operating systems (Unix, Linux, MacOSX etc) are supported. Microsoft Windows is not supported. The current version requires Java 1.8. Note that the Oracle Java is preferred; OpenJDK is not officially supported.
The GATK package is made available for free to academic researchers under a limited license for non-commercial use. If you plan to use the GATK for-profit, you will need to purchase a license. Please see the Licensing page for more information.
The source code for the full GATK package is available in the broadgsa/gatk-protected repository on Github. The source code for the GATK engine, which is open-source, is also available separately in the broadgsa/gatk repository on Github. This includes the engine, infrastructure libraries, Queue and many utility tools. It is intended for developers who wish to develop their own tools, and is freely available to all under the MIT license.