This started out originally as an experiment in using AJAX, which is a technique that allows calls to PHP functions from within Javascript.
The benefit of this being that you can run PHP without having to refresh the browser each time.
I thought I'd give it a go and used the modernmethod SAJAX toolkit to start me off. Things developed pretty well and when I decided to turn this side project into a full game it really worked better than I anticipated.
There were a few little niggles in there that I managed to iron out but even though this isn't the best use for AJAX it did give me a good understanding of what it's capable of and I can appreciate why the big boys like google and yahoo are all using this processing methodology on their new ventures. It's actually one of the first tools/techniques I've used that makes the web browser actually feel like a real product interface.