There’s a good tips and tricks article about CodeRuler on developerworks. The game has a simple premise: You are the imperial ruler of your very own medieval kingdom. Your peasants and knights depend on your brilliant strategic thinking, agile adaptability, and superior Java programming skill to survive, increase, and prosper. Your objective as a player is to write Java code that simulates this ruler. CodRuler is a game that helps you build upon your Java programming skills. CodeRuler is free.