This came up in a discussion in RWT. One poster presented very good arguments about why Sun's releasing of Java under GPL is not as great as it seems because Sun can _at any time_ retroactively change the license, thus closing the source again, making distribution illegal, rendering all derived work created under the GPL illegal too.
Sounds almost like FUD, but check out this explanation by a lawyer, especially the section "Why contracts are better than licences": http://www.ilaw.com.au/public/licencearticle.html
To quote from the article: "In the context of software licensing, this means that there is nothing that can be done to stop the licensor from changing the licence conditions, including makinq them non-free or withdrawing the software altogether. It doesn't matter if an open source licence claims to be irrevocable. Because the licence hasn't been paid for, it isn't."
This is all seriously f*cked up.
There is some more relevant information in this Wired article: http://www.wired.com/news/business/0,1367,35258,00.html (on the second page).
Namely two things:
- The law requires "a written instrument signed by the owner of the rights licensed." So, if you release something under GPL, but you haven't signed a legal document with pen and paper, it is not really valid ??
- Nonexclusive licenses given for free are generally revocable, even if they purport to be irrevocable. Even if the GPL license is treated as signed and is covered by 205(e), it might still be revocable.
Yet more information here: http://en.wikipedia.org/wiki/Public_domain
From David McGowan, Professor of Law, University of Minnesota Law School.
Quoting a little: "Termination of rights
[...] The most plausible assumption is that a developer who releases code under the GPL may terminate GPL rights, probably at will.
[...] My point is not that termination is a great risk, it is that it is not recognized as a risk even though it is probably relevant to commercial end-users, accustomed to having contractual rights they can enforce themselves.
The Free Software Foundations GPL FAQ disagrees with the conclusion I reach here. The FAQ asks rhetorically can a developer of a program who distributed it under the GPL later license it to another party for exclusive use and answers No, because the public already has the right to use the program under the GPL, and this right cannot be withdrawn. 89 Similarly, Lawrence Rosen, general counsel to the Open Source Initiative, has stated (in an FAQ on the SCO/IBM case) that Linux is available free, forever. Neither statement addresses the issue I raise here; I am not aware of the legal basis for either statement. I read them as understandable efforts to keep community members from over-reacting to low-probability risks. That may be sensible real-world pragmatism, a question I leave to the entrepreneurs. As a strictly legal matter, however, these comforting statements are too strong.[...]
What would happen if an author terminated GPL rights? If a single rights-holder held all the rights in the program, then termination would stop future F/OSS development of that program; users would no longer have the right to distribute modified versions of the code, or even unmodified copies of the versions they had."
Botom line: if for example Microsoft bought Sun in a hostile takeover Free Java would be dead. Similarly, if Oracle bought MySQL AB. Or if somebody bought Trolltech. Or if Linus Torvalds died and who ever inherited the copyright to his parts of the Linux kernel didn't care about free software.