p.s. The usage of the word “proprietary” is straight from the FSF.

For instance, none of the Senna, C&C, or LingPipe licenses are compatible with GPL-ed code. Senna goes so far as to prohibit derived works altogether.

Stanford NLP’s license sounds like it was written by someone who didn’t quite understand the GPL. Their page says “The Stanford CoreNLP code is licensed under the full GPL, which allows its use for research purposes, free software projects, software services, etc., but not in distributed proprietary software.” Their wording here makes it seem like “free” or “research” have some special status under the GPL, which they don’t. The terms “research” and “academia” don’t even show up in the license, and although “free” does, although they intend it as “free as in free speech”, not “free as in free beer”:

http://www.gnu.org/licenses/gpl.txt

The basis of the GPL is simple — if you redistribute code based on GPL-ed code, you have to release the redistributed code under the GPL (in some cases, you can get away with using a less restrictive license like LGPL or BSD for your mods or interacting libraries, though you can’t change the underlying GPL-ed source’s license). Stanford’s right in saying you can’t distribute proprietary (by which I assume they mean closed source) code that uses GPL libraries (the meaning of “uses” here is a bit complex, but think of linking in C/C++ terms). You can charge for GPL-ed code if you can find someone to pay you. That’s what RedHat’s doing with Linux, what Revolution R’s doing with R, and what Enthought’s doing with Python. It’s not what MySQL did with SQL or what we do with LingPipe — in both those cases, the company owned all the IP and thus could negotiate for any kind of license they wanted, as well as distributing open source.

You can also set up a software service, for example on Amazon’s Elastic Compute Cloud (EC2) or on your own servers, that’s entirely driven by GPL-ed software, like say Stanford NLP or Weka, and then charge users for accessing it. Because you’re not redistributing the software itself, you can modify it any way you like and write code around it without releasing your own software. GNU introduced the Affero GPL (AGPL), a license even more restrictive than the GPL that tries to close this server loophole for the basic GPL.

With GPL, you just have to abide by the terms of distributing your dependent code with a compatible license. There’s no free ride for academics here — you can’t take GPL-ed code, use it to build a research project for your thesis, then give an executable away for free without also distributing your code with a compatible license. And you can’t restrict the license to something research only. Similarly, you couldn’t roll a GPL-ed library into Senna or C&C or LingPipe and redistribute them under their own licenses. Academics are often violating these terms because they somehow think “research use only” is special.

Also, keep in mind that as an academic, your university (or lab) probably has a claim to your intellectual property developed using their resources. Here’s some advice from GNU on that front:

http://www.gnu.org/philosophy/university.html

http://radimrehurek.com/gensim/