Do you love the puzzle and Linux/Unix-like system? Command line? Try ncurses based Tetris clone which is harder than every other Tetris out there. From the project home page:

Have you ever thought Tetris(R) was evil because it wouldn’t send you that straight “I” brick you needed in order to clear four rows at the same time? Well Tetris(R) probably isn’t evil, but Bastet certainly is. >:-) Bastet stands for “bastard tetris”, and is a simple ncurses-based Tetris(R) clone for Linux. Unlike normal Tetris(R), however, Bastet does not choose your next brick at random. Instead, Bastet uses a special algorithm designed to choose the worst brick possible. As you can imagine, playing Bastet can be a very frustrating experience!