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I often hear about GPL variants, MIT, BSD and many other license options. A general Internet search reveals sites like "Top 20 licenses" or pages some licenses going out of fashion and others coming in.

With so many licenses to choose from, a major stumbling block for beginners in open sourcing is deciding what license to go for.

So, what are the stats on the most frequently adopted open source license options, and what are there primary differences?

closed as too broad by bmargulies, Mark, curiousdannii, overactor, Zizouz212 Jul 21 '15 at 5:34

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    Asking for some stats could be helpful, but asking for a comparison between them all makes this too broad. – curiousdannii Jul 21 '15 at 2:27
  • Good idea, but I thought "most common" basically means, which is the most commonly used in terms of usage, which naturally leads to stats. I was not asking "which is the best", for example, which would be vague and not helpful. But, I think novices really do need a broad understanding of the differences, so that they don't have to trawl through 20+ licenses before making a decision. I've tried to refocus the question. See what you think. – lozzer Jul 22 '15 at 6:29
  • After writing all the above, I thought the first answer was exactly what I was looking for. Great forum! – lozzer Jul 22 '15 at 6:34
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Determining the relative popularity of various licenses is actually quite difficult. Below are two graphs.

The first is taken from BlackDuck: Top 20 Open Source Licenses:

BlackDuck: top 20 graph

and list the following top 5 (making up 76 % av the total):

  1. GPLv2 (24 %)
  2. MIT/Expat (20 %)
  3. Apache 2.0 (16 %)
  4. GPLv3 (10 %)
  5. modified BSD (6 %)

The second one is taken from presentation at the 2013 Linux Foundation Collaboration Summit Licensing of Software on Github: A Quantitative Analysis:

Linux Foundation Collaboration Summit graph

and list the following top 5 (making up 82 % av the total):

  1. MIT/Expat (36 %)
  2. modified BSD (13 %)
  3. GPLv2 (13 %)
  4. GPLv3 (12 %)
  5. Apache 2.0 (8 %)

There is a lot of interesting data in the Linux Foundation Collaboration Summit presentation (e.g. the distribution between permissive, copyleft, weak copyleft and dual licensing, and the shift over time towards more permissive licenses). I recommend clicking through all the slides.

While the source and methodology of these studies differ (and only the presentation made at the Linux Foundation Collaboration Summit explains the methodology used), both list the same licenses as the top five, but their relative position differ.

While these stats are not definitive (and I hope other answers can show us more studies of this type), I think it is quite likely that these licenses are among the most used ones.

As for how "they differ in their most important terms and conditions?", that would make a very long answer. However, the FSF has a very good page about various licenses and comments about them, here are direct links to each of the top 5, with a note stating whether the license is copyleft or permissive - as this by far is the main difference between the FLOSS licenses.

  1. MIT/Expat - permissive
  2. modified BSD - permissive
  3. GPLv2 - copyleft
  4. GPLv3 - copyleft
  5. Apache 2.0 - copyleft, but allows downstream relicensing to GPLv3

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