Multi-licensing and license compatibility for open source projects?

Question

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.

Answer 1

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.

Answer 2

I can answer to your first question.

As far as I know the only 'viral' license is the GPL. There's also the CreativeCommons license with SA clause, but I don't think software is released under that license.

Answer 3

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.