One of the things I really enjoy is playing old games on the Game Boy. Seriously, games were just more fun back then.
One of my favourites was called Tetris Attack. Want to waste quarter of an hour in mental stress? This is an excellent game for you.
It's quite simple really. The board slowly (at first) scrolls up, exposing new pieces. You can select any two neighbours on the same line and swap them over (that really is the extent of what the player can do, apart from accelerating the exposure of new pieces by hitting the space bar). And if you get 3 the same in a line, they're cleared and pieces above can drop down. If pieces reach the top of the screen, the game ends.
As an exercise, I coded this up on a couple of holiday evenings. It's loosely based on the original, but doesn't have anything other than the main endless game mode, and isn't quite as smart or interactive.
You can also just grab the jar file;
depending on your browser and operating system it may run straight
off. If not then just feed it to java -jar, or just run
the jattack script from the main download (which includes
all the source).
Source on GitHub | SVR4 Package for Solaris