Mac OS X Easter Egg - Tetris Hidden in the Terminal

1. Open the finder
2. Open Applications
3. Open Utilities
4. Open Terminal
5. type "emacs"; click enter
6. Press ESC + X at the same time
7. Type "tetris"
8. Play Tetris! Use the arrow keys to move and rotate the blocks, and press the space to make the blocks fall.

This isn't really a part of the Mac OS, it's a part of emacs which is part of the UNIX system. Most Mac users don't know this is included with their computer. There are many more games included as well. To know what other games are included, do the following:
Open the terminal again, at the prompt type:

"cd /usr/share/emacs/"
"ls"

read the VERSION NUMBER of emacs then put this in the command below

"ls /usr/share/emacs/VERSION NUMBER/lisp/play"

In my Mac the VERSION NUMBER is 22.1 so I need type
"ls /usr/share/emacs/22.1/lisp/play"

Don't forget the space!
You'll get a directory of the games included with emacs,
to play these games do the same thing as with tetris,
except type your chosen game's name in place of tetris.