License proliferation

License proliferation refers to the phenomena of an abundance of already existing and the continued creation of new software licenses for software and software packages in the FOSS ecosystem. License proliferation affects the whole FOSS ecosystem negatively by the burden of increasingly complex license selection, license interaction, and license compatibility considerations.

Often when a software developer would like to merge portions of different software programs they are unable to do so because the licenses are incompatible. When software under two different licenses can be combined into a larger software work, the licenses are said to be compatible. As the number of licenses increases, the probability that a Free and open source software (FOSS) developer will want to merge software together that are available under incompatible licenses increases. There is also a greater cost to companies that wish to evaluate every FOSS license for software packages that they use. Strictly speaking, no one is in favor of license proliferation. Rather, the issue stems from the tendency for organizations to write new licenses in order to address real or perceived needs for their software releases.

License proliferation is especially a problem when licenses have only limited or complicated license compatibility relationships with other licenses. Therefore some consider compatibility with the widely used GNU General Public License (GPL) an important characteristic, for instance David A. Wheeler as also the Free Software Foundation (FSF), who maintains a list of the licenses that are compatible with the GPL. On the other hand, some recommend Permissive licenses, instead of copyleft licenses, due to the better compatibility with more licenses. The Apache Foundation for instance criticizes the fact that while the Apache License is compatible with the copyleft GPLv3, the GPLv3 is not compatible with the permissive Apache license — Apache software can be included in GPLv3 software but not vice versa. As another relevant example, the GPLv2 is by itself not compatible with the GPLv3. The 2007 released GPLv3 was criticized by several authors for adding another incompatible license in the FOSS ecosystem.

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