Wolfram is a cross-platform game engine intended for point-and-click adventure games. It also includes a framework for creating your own adventure games.
Galahad is a Java framework for the construction of multi-player card and board games of all types. Galahad will include network and AI play and will ultimately evolve into a set of vertical and horizontal frameworks.
Sudokumat is a software that allows to easily create and solve sudokus of different levels of difficulty. It is possible to create your own "pdf-sudoku-book" with as many sudokus as you want. Every sudoku is solved within milliseconds.
Ataraxia will provide a generic internet gaming framework in java. Board, table, card games will be easy to be developed! bridge, hearts, spades, rummy, go, connect-4, chess, checkers, monopoly, risk, mahjong and more will come! JXTA P2P will be tested.
Learn basic constraint logic programming by solving logic word puzzles. Go to http://eclipse.dougedmunds.com . This tutorial will show you how to solve easy 1 star to hard 5 star puzzles, using the eCLiPSe-CLP language (available at http://eclipseclp.org/).
Don't confuse this programming language (a prolog language) with the IDE for Java.