Hi, and welcome!
These extensions are my contribution to the world of Public Licenses... I love that way of thinking! In short the GNU GPL states that you can use and distribute your copy, modified or not. You may charge for it too... But if you use anything licenced with the GNU GPL, your code must be GPL too! (official gpl license)
Eventually, all my extensions will be offered in 2 versions, free and pro... The full version offering extra features an NO COPYRIGHT LINK !!! The premium subscription cost only 14$ and give you access to pro versions of all of my extensions, unlimited downloads and unlimited number of websites!
If you are downloading my free extensions, I kindly ask that you leave a comment on the Joomla! extensions directory.
I am available for any custumization of existing extensions as well as development of complete solutions... I will make your vision come true!