Linux and Free Software is written by clever programmers. As such, undocumented features creep in to the most mainstream of applications. We call these Easter Eggs, because you have to hunt them.
Here are a few of my favorites.
From the terminal:
aptitude moo -v
aptitude moo -vv
aptitude moo -vvv
etcetera and so on
Take a break from all that number crunching and enjoy a few games in Open Office Calc
Open a new Spreadsheet
In Cell A1 type =GAME(A2:C4;"TicTacToe")
In Cell A1 type =GAME("StarWars")
A couple more Open Office Easter Eggs
In any Calc cell type =TTT() to get a random smiley.
In any Calc Cell type =STARCALCTEAM()
In the Help->About OpenOffice.org Screen Press CTRL-S-D-T
Skype Hidden Chat Emoticons
(I know its not "free", but it is available for Linux, so there)
(london) (mooned) (bandit) (finger) (toivo) (rock) (smoking) (tmi) (heidy)
(poolparty) (bug) (fubar) (drunk) (headbang) (flag:US) (myspace)
Last but not Least, The Best Linux Easter Egg Ever
That's enough for this year. Have a Happy Easter! Feel free leave your favorites in the comments.