Casio Chess
Chess game for the Casio CFX-9850GB PLUS
To my knowledge the first chess game for the Casio CFX that actually works. In the other chess game, popular at that time, it wasn't possible to move the knight, castling wasn't supported and check wasn't checked for correctly.
I went to make a better version which didn't have these shortcomings. The only thing I didn't manage was automatically checking for checkmate. The players needed to check that for themselves when the Casio detected check. Back then, I calculated it would have costed me another 32kb to automatically detect checkmate as well. And the game already took the full 32kb available. Probably, I could make it better with my current knowledge and maybe even fit it all in one 32kb Casio.
Afterwards, unhappy with the playability on the slow Casio processor, I made a light version of the game. It was much smaller, less then 6kb, and used a slightly different interface. Above all, it didn't check for any rules. You can move the pieces anywhere you want and are responsible for playing by the rules yourself.
Made around 2002/2003, I didn't touch the source since then. I can't give any support for it might someone want that. If you want to improve on it, fork for your own pleasure instead of filing bugs or sending pull requests.