PSP Gnu Chess use the GNU Chess version 5.07 for the Artificial Intelligence, and ZUX-81 added a Graphical User interface.

Changes:

– Option to specify search depth (i.e: difficulty)
– Add Undo feature
– Add Book feature, move database is stored in file book.dat.
The file given with this homebrew is the book.dat provided
with gnuchess (but you can replace it by your own)
– Bug fix when you put black on the bottom of the screen,
King and Queen weren’t at the right place !
– Bug fix with keys/analog pad (sensitivity was too high)

http://zx81.zx81.free.fr/serendipity/index.php?/archives/242-guid.html