GPL

GPL, an acronym for the GNU General Public License, is a family of software licenses that are common among FSF developers and many others.

See Also

LGPL
GPL Scripts
the implications of releasing a Tcl script under GPL
ANN: CriTcl 0.18 builds C extensions on-the-fly , comp.lang.tcl, 2001-11-12
a long thread that ended up discussing the merits of the GPL
Google search for "GPL" comp.lang.tcl

Reading

GPL FAQ
official FAQ's
The History of the GPL , Andy Tai, 2001
12 Years of GPL Compliance: A Historical Perspective , Bradley M. Kuhn, 2011-05-13
compatibility overview GPL v3
GPL v1 (1989) license text
GPL v2 (1991) license text
GPL v3 (2007) license text
Common Lisp and Readline , clisp mailing list, 1992-10-19

Description

However it is not at all favoured for the Tcl core, as it severely restricts what commercial development may be done with it. IMHO it works better for applications, and though there is the LGPL (Lesser or Library GPL) and other derivative FSF-sponsored licenses to address these sorts of concerns, Tcl's modified Berkeley license is still the currently preferred (and required for Tcl core work) license.

Interpretation

AMG: Excerpt from a private discussion between W. Young and me regarding the GPL:

(WY) The GPL is more a social construct than a legal construct. The GPL guarantees certain freedoms to the people you distribute your software to. If you don't take away those freedoms, you’re probably good.
(AMG) I view the GPL slightly differently. It's not so much the people who have the freedoms, it's the code itself, if you'll allow me to personify it so. The code itself has the right to be free, and in order to assure that right, the people using and distributing the code must give up the right to create and redistribute non-free derived works. It's a little like if I gave you a bird on the condition that no one can ever keep it or its offspring in a cage. Except thankfully code doesn't usually fly away on its own. Usually.

bll 2017-10-23

I would have to disagree with WY. The GPL takes away my freedom -- it imposes conditions upon my use of the code. I think the BSD and MIT licenses represent freedom better. I find the GPL community's definition of freedom quite strange. Forcing someone to act in a certain way is not freedom. I like your (AMG) take on it better; where the code is /licensed as/has the right to be/ free for use.