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.
If I distribute GPL'd software for a fee, am I required to also make it available to the public without a charge?No. However, if someone pays your fee and gets a copy, the GPL gives them the freedom to release it to the public, with or without a fee. For example, someone could pay your fee, and then put her copy on a web site for the general public.
Does the GPL allow me to distribute copies under a nondisclosure agreement?No. The GPL says that anyone who receives a copy from you has the right to redistribute copies, modified or not. You are not allowed to distribute the work on any more restrictive basis.
If someone asks you to sign an NDA for receiving GPL-covered software copyrighted by the FSF, please inform us immediately by writing to
license-violation@fsf.org.
If the violation involves GPL-covered code that has some other copyright holder, please inform that copyright holder, just as you would for any other kind of violation of the GPL.
Does the GPL allow me to distribute a modified or beta version under a nondisclosure agreement?No. The GPL says that your modified versions must carry all the freedoms stated in the GPL. Thus, anyone who receives a copy of your version from you has the right to redistribute copies (modified or not) of that version. You may not distribute any version of the work on a more restrictive basis.