I just came across this xkcd comic about Real programmers.
I started emacs invoked butterfly command and that's my first easter egg. Later I digged around and found several games & a few other easter eggs. Here are a few of them.
M-x butterfly: Flip the desired bit on the drive platter.
M-x doctor: Switch to *doctor* buffer and start giving psychotherapy.
M-x zone: zone out completely.
M-x life: runs Conway's "Life" cellular automaton.
M-x studlify-buffer: stUdlIfY-RegioN stUdlIfY-CaSeS thE region.
M-x landmark: Start or resume an Landmark game.
M-x animate-birthday-present: Return a birthday present.
M-x yow: Return or display a random Zippy quotation.
Notes:
1. yow was removed in Emacs 22 due to copyright problems. But you can get it manually.
Download quotes file to your .emacs.d directory
M-! wget bit.ly/emacs-yow -O ~/.emacs.d/yow.txt.gz
Specify the path of file in Your init file
(setq yow-file "~/.emacs.d/yow.txt.gz")
2. To know about each of the easter eggs, you can use help
C-h f RET <function> RET
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