Last semester, during the finals, when reading 400 pages on CPU design did not appeal to me I decided to make a game in JavaScript.
It took me 40 minutes to write this and my goal was to make the AI impossible to beat (I failed...)
You should give it a try at http://sasangootik.com/fillr/ (I must warn you, fillr is extremely addictive)
Here are the rules/instructions:
To make it fair computer has 1 rule:
I suck at explaining the rules, just play it and I'm sure you'll get it.