Part of the charm of Emacs is its collection of easter eggs. It contains a tetris clone, Towers of Hanoi, Conway's game of life, and others.
One Easter egg I discovered by accident (through using smex) is:
Which takes an argument (the person's name) and displays an animation wishing that person happy birthday. My favorite Easter egg is
gomoku. It is a fun 5-in-a-row game against the computer.