tetris

The game of Tetris has turned 25 24. I don't care very much about computer games,
but I've nevertheless spent quite a bit of time playing Tetris - its
brilliance is in its simplicity.

Obviously, emacs comes with a Tetris-clone; just type M-x tetris RET and
there you go! There is very little useful things to customize about the game,
except maybe you'd like to keep your ~/ clean and set:

(setq tetris-score-file 
  "~/.emacs.d/tetris-scores")

I'd also like to point to the lisp source code, which is only 658 lines long -
almost CodeGolf-worthy. It's an interesting read if you are that kind of person. To see the source code, access the help for M-x tetris, i.e., press C-h f tetris and Enter (as discussed in Helpful Emacs). You'll get a help buffer then, which includes a link to tetris.el,
the source code; obviously, you need to have the sources installed. In
Ubuntu/Debian, you can install the source code through the emacs22-el or

emacs-snapshot-el packages, depending on the version of emacs you're using.

Thanks to emacs, you can actually read the source code in one buffer, while
playing tetris in the other one!