ZX81 - chess ...only 672 bytes. source code:

http://users.ox.ac.uk/~uzdm0006/scans/1kchess/

Micro-Chess, from 1976, which ran on a KIM-1 (6502) machine and used 1.1K of RAM.

http://users.telenet.be/kim1-6502/microchess/microchess.html

Toledo Javascript Chess Game

http://nanochess.110mb.com/chess4.html

+ TOLEDO JS1K orking demo: http://js1k.com/2010-first/demo/699