A friend of mine asked me to briefly explain the GPL and what made it special. My digest focused entirely on Copyleft .
It took him a while to grok it. How can laws designed to limit and control distribution be used to enforce and compel distribution? Having spent a lot of time in Open Source I sometimes forget how mind bending Copyleft can be to initially comprehend.
For the curious, here’s the MS Word 100 word AutoSummary of the GPLv2:
The GNU General Public License (GPL)
Copyright (C) 1989, 1991 Free Software Foundation, Inc.
(Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) Finally, any free program is threatened constantly by software patents.
6. Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions.
11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.
This General Public License does not permit incorporating your program into proprietary programs.
What? No preamble? Well, at least they got the part about redistribution and something vague about patents threats. And of course they got the part about their being no warranty.