These hidden files are accessable from any unix based operating system, including linux and Mac OS X. To see a list of what there is to offer type -

ls /usr/share/emacs/21.2/lisp/play
into a terminal window (terminal is located in Applications/Utilities)

To play the games, open a new terminal window and type “emacs” and hit return. Once in emacs, press Esc then x to get to the prompt. Now you can type any of the files in the list to play them.

My favourites are:
snake, tetris and pong, the old classics.
doctor, a shrink in your mac (he/she isnt that helpful, unless you threaten to commit suicide)
life, one of the first screen savers.
dunnet, an old text based game where you can explore
zone, makes the text on your screen go crazy

Have fun!