Bastet ("bastard tetris") is an ncurses Tetris clone which is harder than every other tetris released. It is based on a heuristics engine which tries to detect which block you need or don't need, and then gives you the blocks that you don't need. For instance, if you usually play by leaving long "canyons" one square wide and then waiting for the long "I" block, you'll have to wait till eternity before you see it. The heuristics have been worked on for some time and are quite nasty.
The Z-machine Preservation Project is a Java implementation of the Z-machine (Java version >= 5 is required) specification. This Z-code interpreter can be run either as a standalone application or as an applet within a Web browser. It runs Interactive Fiction created by Infocom as well as those compiled with Inform, and targets all existing story file versions. Features include saving the game state, multimedia support (graphics, sound effects, meta data), colored and styled text, undo, and timed input as well as support for different languages. Games in the Inform 7 release format are supported as well (Treaty of Babel specification).
MUSoSu is a free software project for playing, solving, and generating Sudoku games. It is written in Java and emphasizes both solving Sudokus simulating methods used by hyman solvers and generating Sudoku problems that don't require trial and error methods to be solved. MUSoSu is partly themeable and platform independent.