In the past two installments, I suggested a basic icon theme to describe the important points of a variety of Free Software licenses, applied those icons to the top ten most popular Free Software licenses and found that several of them are "the same" in terms of icons -- which suggests that either what the two licenses does is roughly the same (so we can consider them equivalent) or that there is a distinguishing characteristic that hasn't been taken into account yet. The second installment took a close look at two licenses that were "the same" and illustrated a third option: that I'd applied the icons wrongly.

free software source copyleft

One question left over from the first installment is whether the Artistic and LGPLv2.1 licenses are different in a meaningful fashion. I won't try to answer that here, but instead I'll carry on with the next top 10 most popular licenses, as enumerated by Black Duck Software again (bear in mind that these licenses apply to less than 1 percent of all Free Software projects):

  • Common Public License
    free software source patent
    This license has been superseded by the Eclipse Public License, but remains more popular than its successor. It looks a lot like the Apache license, although there's a subtlety in the patent grant ("at the time") and a designation of jurisdiction (New York). It is weak copyleft, because it requires source to be made available in a reasonable fashion, but certain additions to the program are excluded.
  • Eclipse Public License
    free software source patent
    It is very difficult to see what the difference is between the CPL and EPL. I don't feel like running diff right now.
  • zlib
    free software
    The zlib license adds to the basic 1-clause or 2-clause MIT / BSD licenses a requirement to mark changed files and to represent the origin (and modification) of the software accurately. I consider that a common courtesey and basic honesty, but it might be good idea to add it to the list of icons; a kind of "label the provenance" image (but I can't think of one right now).
  • LGPLv3
    free software source copyleft embedded patent grant
    The LGPLv3 is interesting because it is relatively short: it is explicitly a "GPLv3 with these additional permissions and modifications to the conditions".
  • Academic Free License
    free software source patent
    Interpreting Larry's licenses leaves me a little scared: it is, after all, his specialty to write licenses. I don't see how this is copyleft, since there is no obligation to provide source downstream -- unless I'm totally misunderstanding the meaning of "contradicts" in clause 1.d. The license itself allows non-contradictory re-licensing; that probably deserves an icon of its own, although I suspect that relicensing is going to be possible only within the group of licenses with the same set of icons (I'd hope so). There is some specific patent and retaliation language here, but the troll in the "patent grant included" icon should make everyone read twice.
  • Open Software License
    free software source patent
    Another Larry Rosen product, and the only difference I can quickly spot is that this one requires licensing derived works and copies under the same license (where AFL allows a different but non-contradictory license). More evidence for the need for a "allows relicensing" badge.
  • CDDL
    free software source copyleft patent grant
    Largely the same as the Mozilla license.
  • Mozilla Public License 1.0
    free software source copyleft patent grant
    Largely the same as the Mozilla license. Oh, wait, this is the Mozilla license, just an earlier version. I don't feel like breaking out diff just now.
  • PHP
    free software
    The PHP license looks at first glance like a BSD-style license; and then you realize it has six clauses instead of 2 or 3 (four thou shalt not count; five is right out). These have to do with the use of the name PHP and as far as I'm concerned would justify a kind of warning badge saying "surprise conditions here". I'm not going to draw one just right now.
  • Ruby
    free software source
    This is an unusually permissive license because it allows relicensing or public domain distribution and allows binary distribution while pointing only to the original.

That wraps up the tour of the top 20 most popular Free Software licenses, good for pver 90 percent of all software licenses in the Free Software world (though apparently there's about 1800 variants out there). Today's list suggests that we need an additional badge for relicensing, one for "watch out!" and perhaps a "represents" badge as well.

So, to return to the original reasons for doing this exercise: provide a quick overview of what the licenses mean that we use regularly in the form of an iconic representation, and to illustrate where the essential points of licenses agree. Tomorrow: wrap-up, table presentation, and a general request for better artwork.