The Foundations of the GPL
Nobody should be restricted by the software they use. There are four freedoms that every user should have:
the freedom to use the software for any purpose,
the freedom to change the software to suit your needs,
the freedom to share the software with your friends and neighbors, and
the freedom to share the changes you make.
The first freedom guarantees that you can use the software as you wish, for any work, either it’s commercial, or personal, or non-profit. Works made with the help of our tools are yours and you can do what you want with them.
You don’t need any authorization or contract. Download, install, have fun!
Just know that we’re very curious to see what you’ve made with our tools, so you can send us the result of your work! You can help the developement of the free tools too, with a donation or buying some items in the shop.
The second freedom lets you change the software as you need. You can get the source code on github.
The third and fourth freedoms let you share our tools and distribute them yourself, with or without your changes. However, in order to keep those four freedoms, the GNU General Public License restricts the release of the tools (including your changes) under a compatible license, one which guarantees these four freedoms too. Thus, you can neither sell the tools, nor keep the source code private. You must list all the authors of the free software you share and change too. In short, the tools, with or without changes, must stay free.
If you include any part of the source code of our tools – even a short part – in your own tools, they must be released under a free software license too. You cannot sell any software including some code licensed under a free license.