Minimalism is big. We’ve got 5k chess (an entire game of chess written is less than 5 kilobytes of JavaScript). We’ve got Lego versions of the Old Testament. We’ve got presidents with tiny cardboard facsimiles of a real brain. But here’s one that really blew me away: a tiny version of the old arcade game Defender. And when I say tiny, I mean crazy tiny like building a house on the head of a pin tiny. This is Defender in the space of a 16 by 16 pixel icon. That in itself is impressive, but this guy gets extra credit for making a playable game of Defender run in the favicon space for the browser.
Rambles Blog at Star Chamber 
I just tried a game against the 5k JavaScript chess game. It applies an interesting strategy. Specifically, it ignores that the fact that it has lost the game. When checkmated, it just keeps moving anyway. :-)
The IF clause to see if it lost would push it just over the edge into 5.01 kB, so they had to cut it. If it wins, on the other hand, it plays a little song and runs an animation.