Roll the dice
Not a command, but a fun thing anyway. What if you need a dice (as I needed the other day while trying to play a game with my friends) and you don't have one?
Bash can do it:
$ while true;do let dice="$RANDOM % 6"; let dice=$dice+1;echo $dice;read;clear;done
Though it's a long line, this is just an infinite loop in which we use the $RANDOM bash variable which generates a random number between 0 and 32767. After that, we divide it by 6 and take the remainder (so we have a number between 0 and 5) and add 1 to shift the interval ...