mvlcek wrote:A plugin or theme author may choose to charge money for his plugin or theme, but it will still be licensed under the GPLv3 and thus each buyer can redistribute it to the public with or without charge.
Not true. You, as a plugin author, can licence your work however you wish and under more than one licence at the same time (though not more than one licence in the same distribution package at the same time). So, you can have a GPL version and a proprietary licensed version, though that doesn't make a lot of sense with a PHP script unless you go for encryption (e.g., Zend Guard or similar). These could be versions with the same capabilities (not much point) or a free version and a commercial, enhanced, version.
You must make the source code of the GPL version easily available as long as the program is available and there would be nothing preventing a third party from adding in features (including features reverse-engineered from your commercial version) or taking control of a forked version under a new name. You would still Ã¢Â€Â“ and forever Ã¢Â€Â“ have copyright in your original GPL'd code and you must be credited for that, even when it appears in the forked, re-named version.
In the general arrangement of a core program and plugin enhancements, that's a whole new grey area. AFAIK, there's nothing to prevent a proprietary plugin from being used with a GPL application, but you wouldn't be able to distribute a single package with proprietary plugin and GPL core compiled together or have proprietary code included in a GPL product.
I emphasise, this is not legal advice, but an informed opinion.
Connie wrote:al these points are important. But in the moment I see not enough manpower to check and to take care that all plugins and themes are license-compliant
Yes, they are important Ã¢Â€Â“ legally binding important. The only thing that the GetSimple executive has to be concerned with, is the licensing of GetSimple and seeing to its compliance with the licence terms. Plugins and themes are the responsibility of their respective authors.
That said, I haven't seen much evidence of licence or copyright statements in either plugins or themes, not that it's essential, but it's certainly prudent for the author.