GNU General Public License
Introduction
The GNU General Public License (GPL) is a widely used free software license, which guarantees end users the freedom to run, study, share and modify the software. The license was originally written by Richard Matthew Stallman for the GNU Project in 1989, and grants the recipients of a computer program the rights of the Free Software Foundation's four freedoms.
History
The GPL was created by Richard Stallman in order to protect the software produced by the GNU project from being proprietary. The first version of the GNU General Public License, released on 25 February 1989, was written by Richard Stallman with legal advice from Eben Moglen. The second version of the license, version 2, was released in 1991. Over the following 15 years, members of the Free Software Foundation worked on revising the GPL's language to address new forms of software distribution. In 2007, the third version of the license (GPLv3) was released to address some of the problems identified with GPLv2.
Terms and Conditions
The terms and conditions of the GPL must be made available to anybody receiving a copy of the work that has a GPL applied to it ("the licensee"). Any licensee who adheres to the terms and conditions is given permission to modify the work, as well as to copy and redistribute the work or any derivative version. The licensee is allowed to charge a fee for this service, or do this free of charge. This latter point distinguishes the GPL from software licenses that prohibit commercial redistribution.
Compatibility and Multi-licensing
The GPL is designed to ensure that the software under the license remains free, and that the source code be available to the users. Therefore, the GPL is incompatible with software licenses that do not require distribution of source code with binaries. However, software can be multi-licensed under several different licenses, including the GPL, so that recipients can choose under which terms they want to use or distribute the software.
Adoption
As of 2015, according to Black Duck Software and Synopsys, Inc., the GPL family of licenses are used in nearly 70% of all open source software. Notable companies and projects that use the GPL include the Linux kernel, MySQL, and the GNU Operating System. The adoption of the GPL could be attributed to the growth of the Internet, and the attendant need for massive retooling of the computing infrastructure, which companies like IBM and HP have invested billions in.
Criticism
While the GPL license is widely used, it has also been subject to criticism. Some developers believe that the GPL is too restrictive, and prefer to use more permissive licenses. Others have criticized the GPL as being "viral", in that any software that links to GPL-licensed software must itself be under a GPL-compatible license, which can prevent its use in proprietary software.