You can read the complete license at the official websites of the GNU project:
The GNU General Public License Version 3.
The main idea of the license is: Feel free to use the software, edit the software, integrate it in your commercial or non-commercial websites or products and distribute the software. When you choose to distribute the software the receiving party will automatically receive the same rights.
You don't have to release the source code of your software, which you don't distribute to the end users (typically server side scripts in PHP, ASP, Python, etc.). The license is not affecting any data which are used with the software.
We welcome anybody to cooperate on the development of this project. Please read How to contribute.
The copyright on the source code is hold by the original creator of the project and the maintainer: Klokan Technologies GmbH. We keep the right to provide the software under a different license to interested developers.
We guarantee that the project is always going to be available as open-source and as free software.