John T. Haller, Updated May 11, 2014 (Created August 28, 2009)
Popularity of individual open source license usage is tracked by several entities with the results published online. I thought it would be interesting to combine the license types that are similar and map out the overall popularity along with OSI and FSF approval and GPL compatibility. As you can see, the GPL/LGPL is the most popular license by a wide margin with over 45% of software being licensed under one or more versions. The next 3 licenses are all GPL compatible in some way meaning 67% to 87% or more of all open source code is GPL compatible and can be added to GPL licensed projects. Note that you can't tell exactly as some version issues enter into the mix with the Apache and Perl licenses.
| License | Percent | OSI Approved | FSF Approved | GPL Compatible |
|---|---|---|---|---|
| GPL/LGPL (2 & 3) | 45% | Yes | Yes | Yes |
| New BSD / MIT | 22% | Yes | Yes | Yes |
| Apache License | 15% | Yes | Yes | Yes (GPL3 Only) |
| Artistic License (Perl) | 5% | Yes | Yes (2 Only) | Yes (AL v2 Only) |
| Microsoft Public License (Ms-PL) | 2% | Yes | Yes, but...* | No |
| Eclipse Public License (EPL) | 2% | Yes | Yes | No |
| Code Project Open License | 1% | No | No | No |
| Mozilla Public License (MPL) | ~1% | Yes | Yes, but...* | No (Unless Specified) |
| zlib/libpng License | <1% | Yes | Yes | Yes |
Statistics from Black Duck Software from May 11, 2014.
* the FSF recognizes the license as a free software license but recommends against using it