A debate has raged for months about open source licensing trends. It all started with assertions that the GNU General Public License (GPL) is rapidly falling from favor as an open source license, replaced largely by the Apache License. Free software advocates couldn't disagree more.
What's really going on? To understand the answer, you need to know a little background.
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A capsule history of open source licensing
The GPL is by far the most widely used copyright license. It's intended to deliver the "four freedoms," where end-users are free to use, study, modify, and distribute GPL-licensed software for any purpose. It's associated with the "free software" movement, started by Richard M. Stallman in the early '80s and now embodied in the Free Software Foundation (FSF).
The first version of the GPL was written by Stallman in 1989, and it's since been updated twice, most recently to add protections against software patents. It's notable for the controversial way it is crafted to achieve Stallman's goal of creating an ever-growing pool of GPL-licensed free software by requiring that any other programs combined with GPL titles also have its copyright licensed under the GPL. This "copyleft" approach is the essence of the GPL's controversial nature; some people consider it wrong to make access to the software conditional on allowing others the same access.
Significantly, the GPL is used to license the Linux kernel and is credited with creating a uniform licensing environment in which software from many sources -- including Stallman's own GNU Project -- could be combined to create a working operating system. As the resulting "GNU/Linux" operating system rose to prominence, a great deal of software became available under the GPL. It became the default choice for software developers creating new packages, less for its associated ideology and more for its compatibility with GNU/Linux.
Another thread of software freedom stretching back just as far uses a different approach that eschews any "copyleft" requirement. Most of Stallman's peers decided to license the copyrights to their software in a very relaxed fashion, giving anyone who received the source code the right to use it as if they owned it, with very few restrictions.
Originally associated with variants of Unix, these "permissive" licenses took their names from the universities at Berkeley and Massachusetts: the BSD and MIT licenses. These licenses allow you to do almost anything with the associated software, including making it closed, proprietary software to which the four freedoms no longer apply. This is also a source of controversy, as some people consider it wrong to take open source software and prevent others in the future from using, studying, modifying, and distributing it.
Over time another permissive copyright license has become very widely used. Associated with the large and successful Apache Software Foundation, the Apache license is similar to the earlier BSD and MIT licenses but has added protections for the communities using it, notably related to software patents. Both the Apache license and the GPL have spread independently of their associated communities, and they've been joined by a range of other copyright licenses crafted by different communities for different purposes. The Open Source Initiative (OSI) was established in 1998 to validate whether such licenses truly delivered software freedom, using the "open source definition" as its rubric.
The case for the GPL's decline
The idea that the GPL is in decline appeared last summer when 451 Group analyst Matthew Aslett built on comments defending Oracle's open source adjustments by Eclipse Foundation representative Ian Skerrett. His blog posting used data gathered by Black Duck, a firm providing due diligence services to companies concerned about open source licensing fears. He wrote: "According to Black Duck's figures the proportion of open source projects using the GPL family of licenses has fallen to 61% today from 70% in June 2008, while the GPLv2 has fallen to 45% from 58% three years ago."
The cause of the decline was not the relicensing of existing projects; that rarely happens, and as Aslett noted, the actual number of GPL-licensed projects had increased. But a larger proportion of new projects were choosing permissive licenses. Aslett returned to the topic in another blog in December. His focus remained on the interactions comprising commercial exploitation of open source software, and he predicted the trend continuing.
The case for stasis
As analyst Stephen O'Grady pointed out at the time, the GPL is still a more widely used open source license than the MIT, Artistic, BSD, Apache, MPL, and EPL options all put together. Aslett's assertions raised the ire of the free software supporters, who mounted a defense at the FOSDEM conference in Brussels in February.