What is copyleft?
Discussions of copyleft versus permissive licensing always seem to cover the same “freedom for users versus freedom for developers” clichés and the same tired slavery metaphors.<p>My dislike of copyleft is emphatically not because I want to enable proprietary software. I hate proprietary software, and don’t use it on my machines.<p>No, my biggest complaint about copyleft has always been that it prevents <i>other free software</i> from being able to use it. Copyleft licenses actively lead to incompatibility.<p>Remember when LibreDWG, an AutoCAD file parser, couldn’t be used in various free software CAD projects, because LibreDWG is GPLv3+ and FreeCAD, etc were GPLv2 only? <a href="http:&#x2F;&#x2F;libregraphicsworld.org&#x2F;blog&#x2F;entry&#x2F;libredwg-drama-the-end-or-the-new-beginning" rel="nofollow">http:&#x2F;&#x2F;libregraphicsworld.org&#x2F;blog&#x2F;entry&#x2F;libredwg-drama-the-...</a><p>If FreeCAD had been under a permissive license, it would have been able to link against LibreDWG. If LibreDWG had been under a permissive license, FreeCAD would have been able to link against it. If they were <i>both</i> under a permissive license, they would have been able to be linked together <i>and</i> share code directly!<p>How about when NYC released open building and address data? A laudable move, one that helped several open source projects, the largest probably being OpenStreetMap. OpenStreetMap is under a copyleft license, and though they benefit from NYC’s data, due to the licensing NYC can’t make use of OpenStreetMap’s improvements without a convoluted parallel construction scheme: <a href="https:&#x2F;&#x2F;www.openstreetmap.org&#x2F;user&#x2F;lxbarth&#x2F;diary&#x2F;23588" rel="nofollow">https:&#x2F;&#x2F;www.openstreetmap.org&#x2F;user&#x2F;lxbarth&#x2F;diary&#x2F;23588</a><p>A common response is that the onus is on NYC to release their data under a copyleft license so they can benefit. But there are often significant (even legislative!) barriers to doing that, especially in the United States where government entities are often required to release data to the public domain. How about changing that legislation? Well, if you had initiated such a legislative reform just a few years ago OSM would have been under the Creative Commons BY-SA—which is incompatible with OSM’s current license, the ODbL.<p>Remember how much grief has resulted from the unclear (or perhaps too clear) licensing status of ZFS on Linux?<p>Releasing software and data under the freest, most permissive license possible prevents such a thing from ever happening. I would rather allow a hundred Chinese featurephone vendors to lock down their crappy derivatives of my code than use my copyright to prevent a free software project from using my code in good faith.