licensing and license compatibility for open source projects?
I'm starting a software project that I'd ultimately like to release as free, open-source and free of charge.
My software makes use of other free/open-source software, like Markdown (released under a BSD license), Blueprint CSS (released under an MIT license), and others that use various licenses (GPL, etc.). Some are copyleft, some are not.
I will also choose a license for myself. (Haven't decided yet, but I do have plenty of resources for comparing them.)
I would like to know if there are any resources for navigating the confusing world of license compatibility. I've googled but haven't found much. I know that some licenses are 'GPL-compatible', but I would like to know:
1) Which licenses require derivative works to be released under the same license?
2) Which popular licenses are incompatible with each other?
3) Is there anything you can do in that case other than abandoning your hopes and dreams or reinventing the wheel?
4) I've read that releasing software under multiple licenses allows the user to pick the license terms that they prefer. Must it be that way? What if I have two compatible licenses but I need to release my software under both of them because some code I've used requires that based on its licenses?
If it changes anything, this software is for an academic project.
I'm a programmer, not a lawyer! I'd appreciate your help.
1) Which licenses require derivative works to be released under the same license?
The GPL. No other commonly used license (that I am aware of) requires this.
2) Which popular licenses are incompatible with each other?
As you are using GPL code, you only need to worry about what is compatible with the GPL license (because your code must also be GPL'd) - there is a list here.
3) Is there anything you can do in that case other than abandoning your hopes and dreams or reinventing the wheel?
You should not have any problems, just use the GPL license.
4) I've read that releasing software under multiple licenses allows the user to pick the license terms that they prefer. Must it be that way? What if I have two compatible licenses but I need to release my software under both of them because some code I've used requires that based on its licenses?
You won't have that problem - just use the GPL.
If it changes anything, this software is for an academic project.
It doesn't.
I think the above answers slightly oversimplify. Some open source licenses are not compatible with one another, even though they may be very permissive.
For example I believe that the the GPL is not compatible with the Apache version 1.1 license or the original BSD license (which is not around much any longer).
The XFree86 1.1 License is incompatible with Version 2 of the GPL because because of its requirements that apply to all documentation in the distribution that contain acknowledgements.
The GPL is not the only "viral" (properly known as copyleft) license, although it is by far the most common. There are a LOT of different licenses and needing a lawyer -- or at least an expert -- is not out of the question if you need to combine many of them for a $erious project, but in general the popular open source licenses are all pretty liberal.
I am not a lawyer either. However:
My understanding is that if your code uses GPL code, your project needs to be released as GPL.
GPL requires derivative works to be released under the same license.
You should have no trouble including the (more permissive) MIT / BSD licensed code from a GPL project.
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