This is a fun little trick for anyone on a Mac. If you want to play Tetris, go to Applications >> Utilities >> Terminal
When the Terminal window pops up, type: emacs
To display the M-x prompt, press the key combo [ESC][X]. At the prompt, type: tetris
This tip is part of emacs, a text editor you'll find in most Unix-based systems.
If you want to play a bunch of other games in the Terminal, check out this piece I wrote for BYTE here.