ایضا در مورد فروش:
http://www.gnu.org/philosophy/selling.html

همچنین است:
 Does the GPL allow me to charge a fee for downloading the program from my site?

    Yes. You can charge any fee you wish for distributing a copy of the program. If you distribute binaries by download, you must provide "equivalent access" to download the source--therefore, the fee to download source may not be greater than the fee to download the binary.


اما:


 Does the GPL allow me to require that anyone who receives the software must pay me a fee and/or notify me?

    No. In fact, a requirement like that would make the program non-free. If people have to pay when they get a copy of a program, or if they have to notify anyone in particular, then the program is not free. See the definition of free software.



    The GPL is a free software license, and therefore it permits people to use and even redistribute the software without being required to pay anyone a fee for doing so.



اینم بخونی بد نیست:
Can I write free software that uses non-free libraries?
If you do this, your program won't be fully usable in a free environment. If your program depends on a non-free library to do a certain job, it cannot do that job in the Free World. If it depends on a non-free library to run at all, it cannot be part of a free operating system such as GNU; it is entirely off limits to the Free World.

So please consider: can you find a way to get the job done without using this library? Can you write a free replacement for that library?

If the program is already written using the non-free library, perhaps it is too late to change the decision. You may as well release the program as it stands, rather than not release it. But please mention in the README that the need for the non-free library is a drawback, and suggest the task of changing the program so that it does the same job without the non-free library. Please suggest that anyone who thinks of doing substantial further work on the program first free it from dependence on the non-free library.

Note that there may also be legal issues with combining certain non-free libraries with GPL-covered Free Software. Please see the question on GPL software with GPL-incompatible libraries for more information.