GMChess program is write by gtkmm and c++. it release under GPLv2 . and the chess engine base on xqwizard, which on http://sourceforge.net/projects/xqwizard/. the xqwizard also release by GPLv2. and gmchess copy some picture and some files(example like book.dat). you can see the GPLv2 detail on file which name COPYING in source code.