Good and bad licence changes
Changing from a copyleft licence (e.g. GPL) to a weak copyleft (e.g. LGPL) or to a permissive licence (e.g. Apache License) is almost never a good idea.
The rare situations where it's a good idea
Using a weak copyleft or a permissive licence can be a good idea if:
- the functionality of the software is already widely available in proprietary software; AND
- wide adoption will help break a form of control that proprietary software companies have on a domain (i.e. via a format or protocol); AND
- the copyleft provisions are reducing adoption
Ogg Vorbis and Theora
The Ogg media suite is an example of when it's good to use a permissive licence.
A seemingly bad change:
- Left wondering why VLC relicensed some code to LGPL, Bradley M. Kuhn
Bradley Kuhn says QT's GPL -> LGPL switch was a good move: LGPL'ing of Qt Will Encourage More Software Freedom
status.net and pump.io
status.net was AGPL v3, but the developers chose Apache License 2.0 for the next generation replacement, pump.io. The lead developer, Evan Prodromou says the change is because the software fits the three criteria mentioned above.
LibreOffice (LO) was originally LGPLv3+ but has switched to MPL2. More precisely, it will be dual-licensed under both, but distributors can only be held to the weaker of the two sets of requirements, which is MPL2.
Is this justified? Maybe.
Most of the functionality in LO was already made available under permissive and proprietary licences by Sun Microsystems and later by Apache Open Office (AOO). This puts LO in a weak position because if they ask third-party projects to abide by the weak copyleft requirements of the LGPL, the third-parties have the option of saying no and working with AOO instead. (More info about this race to the bottom can be found in the replies to this comment: .)
"there are plenty of other C libraries; using the GPL for ours would have driven proprietary software developers to use another" as explained in Why you shouldn't use the Lesser GPL for your next library.
GCC runtime libraries
An example of crafting narrow GPL exceptions to address particular use cases rather than moving to a weaker copyleft or permissive license wholesale; in depth explanations by Bradley Kuhn and in the GCC runtime exception FAQ and rationale.
- Why you shouldn't use the Lesser GPL for your next library, GNU Philosophy
- Copyleft: Pragmatic Idealism, GNU Philosophy
- Why Copyleft?, GNU