The game is played inside a web browser and requires WebGL support, so you need a rather new browser (e.g. Google Chrome 9+ or Firefox 4 - IE won't work). Also, your graphics card needs to be at least OpenGL 2 capable (with decent drivers) for WebGL to work. You can check supported browsers and other notes in Khrono's WebGL Wiki.
Start playing by navigating into the game subdirectory.
If you are interested, you can read how the 7-day development went and other retrospective notes here.
The starting point for this game was a wonderful WebGL tutorial by Giles Thomas @ learningwebgl.com. The content there is licensed Creative Commons Attribution/Share-Alike license. There are only few small bits left from the original tutorial code, but to avoid pain with licensing jungle, I'll release this for the time being under the same CC-BY-SA license (even though it's not really a software license), with attribution to here and learningwebgl.com.