You must abide by the gpl license, which means you must include the complete source code of your game. If you want to release a commercial game with out source you need to contact Thomas or Jens to request information about purchasing a commercial use license.
Developing away on one of
Multiple Macs running 10.6, 10.7, 10.8, and 10.9.
Linux, 8-core AMD, 8GB RAM, Fedora 18, nVidia 450 1GB