Kay Hornig has released a chess game for GBA.

Here are his release notes:

After a while developing I’m proud to present my first public project called chessyka.
It is a chessgame. The main goal was not to made the next award winning chessgame. I just wanted to learn developing for the gba and I learn better if there is a real application as a playground.
Now this is the result of my study.

The AI use alpha-beta-search, 0x88 and bitfield representation of the board, hashing with zobrist keys and moveordering. There is an opening book included, but currently this is only a proof of concept and contain only some minor variants of the french defense. A special feature is the possibility to enter a custom position. Although there is only a very simple check for plausibility!
chessyka is aware of all chess rules, including “en passant”, castle, 50-moves-draw and 3x-repetition-draw.

Currently only the english language and basic undo of moves are activated. The multilanguage menu (english, german and espanol) and the advanced undo/redo feature are disabled.

There are some missing features e.g.: permanent brain, search depth extensions and an opening book which is worth the name. If I find the time and motivation I will try to add more of them.

I suggest the level 4 for the AI. Lower is probably to weak and higher needs to much time. A level is a combination of time and search depth. On level 4 chessyka will search at depth 4 (plys) but uses at maximum 2 minutes per ply (average). Which means it will use a part of the spared time from previous moves (e.g. from using the openening book). On level 5 it use 3 minutes per ply average. If you can afford this, it is obvious better.

Maybe later I also present the sourcecode, but not at the moment. chessyka was completely developed by myself. The same applies to the artwork. Only the charset was borrowed from auby.no with his kind permission.
For developing I used the DevkitPro toolchain, the tonclib and “Visual Studio 2003 standard” as an editor.
I want to thank the whole gba homebrew community. Especially I want to thank (in no particular order) Tepples, Cearn and Wintermute!
chessyka was succesfull tested with no$gba (thanks to Martin Korth), “VisualBoy Advance” and of course on real devices: GBASP and NDS lite. For the real devices I used the “EZF advance”, GBAMP v2 CF and Supercard mini SD.

!! Attention !!
chessyka is for evaluation purposes only! Use it at your own risk. There is no warranty, expressed or implied. I’m not responsible for any damage as a result of the usage of chessyka. You are allowed to use and copy the game only in a private environment. You are not allowed to use it on commercial base! With the download you accept this terms of use!

Thanks to http://www.dcemu.co.uk for the news.

http://www.khornig.de/chessyka/gba.htm