Sadly the art and sound effects are not fully GPL yet. I had one person helping me create graphics, but he started a mastery in science, and another friend of mine also gave me some pixel-art and then vanished into limbo :-/
So I'm using copyrighted art fro now, as I am a developer, my art is my code, and I found no one to contribute with free graphics. After I finish the code, I can spare time to create my own art in all places needed and make it fully GPL, but until there, the priority is the code.
If you know about anyone wanting to create pixel-art for a game (for free, of course), please contact me