The Mac comes with a version of emacs that includes several classic terminal-based games. To check these games out, first open a terminal window (applications --> utilities --> terminal). To play a game in emacs, you type emacs and hit Enter, this starts the emacs editor. Once emacs has started, hit the Escape and X keys at the same time, and then type in the name of the game you want to play.

To find out the games that are available, look in the directory /usr/share/emacs/VERSION/lisp/play where VERSION gets replaced with your actual emacs version. In my case, this is 22.1. If you do an ls of this directory (ls /usr/share/emacs/22.1/lisp/play) you'll see a list like so:

listing of the /usr/share/emacs/22.1/lisp/play directory

Each game has two entries, one with a .elc extension and one with a .el.gz. extension. To play the game in emacs, type just the name of the game without any extension after hitting Escape X. For example, tetris, snake, life, gomoku, etc.

You're then well on your way to having a whole new library of classic games available on your Mac.