The original FOSS license.
- "The licenses for most software and other practical works are designed to take away your freedom to share and change the works. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change all versions of a program--to make sure it remains free software for all its users."
- - GPL V3
The key innovation of the GPL license was the requirement that source code be provided along with any binary code distributed, ensuring that the recipients would have the freedom to modify the code themselves for any purpose they wished. This feedback loop was intended to be an innovation engine for a field believed to hold more in common with mathematics than industrial design, and where the possibilities for humanity were nearly endless and the benefit of many hands great.
The idea that GPL binaries cannot be sold or commercially supported for any amount the market will support is a misconception. As Stallman explains it, the GPL means free speech, not free beer. As a high profile example, the original large commercial beneficiary of this license has been Red Hat, which has sold binary related services for their packaging of the GPL Linux operating system and done very well since 1993, perhaps the key player in the early years helping Linux become established in the server space. Indeed, by revenue and community size the most successful FOSS remains that under the GPL, such as Linux, due to its ecosystem generating nature.
Version 3 of the GPL added protections against use with software locking.
The Lessor GPL (LGPL) is more flexible than the GPL, enabling one to "combine or link" with LGPL code without having the linked code also become subject to the GPL. It is mainly meant for operating system and library type linking, but is also used sometimes by those that wish to provide even more freedom to incorporate their software in large systems. The level of restriction if so small that it approaches the near complete freedom of the BSD License. The relevant text added to the GPL is shown below.
"As an exception to the Sections above, you may also combine or link a "work that uses the Library" with the Library to produce a work containing portions of the Library, and distribute that work under terms of your choice, provided that the terms permit modification of the work for the customer's own use and reverse engineering for debugging such modifications."
The master copies are found here www.gnu.org/copyleft/gpl.html.