Project CodeRacers is a game geared for creative java programmers. It's main idea is that each player will create an own AI agent (the so-called "driver"). The user's driver then will compete against other players' drivers in a simulated car race.
JGames is a sort of "game development framework" that creates a solid general structure for all Board Games, Strategy Games and all these game, 2D and 3D, that can be specified defining its particular Rules.
Katz und Maus is a great Java simulation of two animal species, cats and mice. In the game the user can give his chosen species artificialintelligence. In fact he decided about mice he must code how they react on different events, e.g. corn found.