PSP homebrew developer Zx-81 has just released an update for PSP GNU Chess. This game's latest build carries new bug fixes, and a new book features among other things. Here's the full changelog for version 1.0.2:

* 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)

In case you're wondering, this homebrew game is a PSP port of GNU Chess, a command line Chess program that's also been ported to platforms such as UNIX, Windows and Mac OS X. The original version was developed by Stuart Cracraft back in 1986. This PSP version in particular uses GNU Chess version 5.07 for its AI. We advise the readers to view the readme included in the file bundle for full installation and usage instructions.