I recently came across the game Dopewars(or more generically, Drugwars). Now this is an extremely simple game to implement. A trivial basic implementation could be done in a couple of days, at the most. And it's extremely extendable.

Now, my question is what other games are out there that follow this same kind of "difficulty level" for implementation? A game that is actually entertaining, yet trivial to implement, and can easily be extended?