Macaulay 2 is copyright by Daniel R. Grayson and Michael E. Stillman. We permit you to use its source code under the terms of the GNU General Public License, version 2 or version 3, as published by the Free Software Foundation; see the file gpl-2.0-standalone.html or the file gpl-3.0-standalone.html. The Macaulay2 packages by various authors are individually licensed, as are the third-party subroutine libraries linked with Macaulay2 and the third-party programs. The binary executable named "M2" is licensed to you under just version 3 of the GNU General Public License, because it is linked statically with some subroutine libraries not licensed for use under version 2.