StateS is released under the GNU General Public License Version 2.
License text is available in file LICENSE in sources.
StateS include third party art under open licences.
Please refer to the AUTHORS file in art folder of source code.
To obtain StateS source code, use git with the following command:
$ git clone git://git.code.sf.net/p/states/code states-code
Qt 5 is required to build the project, as well as a C++ compiler that supports the -stdC++11 flag (GCC is just fine under Linux).
I use Qt Creator to edit the project, so you can open the StateS.pro file using that tool.
To just build without using Qt Creator, execute:
$ qmake StateS.pro
$ make