Here are some notes about the current state of the licensing of our libraries.
Our license statements are in the files:
    M2/INSTALL
    M2/Macaulay2/d/startup.m2.in
    M2/distributions/cygwin/Macaulay2.README.in

libraries linked with M2:

-lfac		singular libfac		GPL 2 or 3
-lcf		singular factory	GPL 2 or 3
-lntl		ntl			GPL 2 or later
-lgdbm		gdbm			GPL 2 for version 1.8.3, which we currently link with
					GPL 3 for version 1.9.1, which we could link with
-lgc		Boehm gc		"Permission is hereby granted to use or copy this program for any purpose,  provided the above notices are retained on all copies."
-lmpfr		mpfr			Lesser GPL 3 or later
-lfrobby	frobby			GPL 2 or later
-lpari		pari			GPL 2 or later
-lmpirxx -lmpir	mpir			version 2.4.0 : Lesser GPL 2.1 or later
	 	lapack			copyright by U Tennessee under a liberal license
		blas			no license file provided, probably public domain

code by other authors compiled as part of M2:

Macaulay2/kernel/bibasis		Mikhail V. Zinin, GPL 2 or later
Macaulay2/kernel/mixed-cells		Anders Jensen and Anton Leykin, under development, not linked yet with M2
Macaulay2/e code by Franziska Hinkelmann 		public domain
Macaulay2/e code by Anton Leykin			public domain
Macaulay2/system code et al., by Bill Furnish		public domain

Note: according to the chart at

      http://www.gnu.org/licenses/gpl-faq.html#AllCompatibility

LGPL 2.1 is compatible with GLP 2.


Final analysis: for M2 binaries,

      we are prevented from using GPL 2 by mpfr
      and we have to be careful about gdbm

