Vim is text editor built to create/modify text based files. It is quite powerful and customizable.
Vim can be used on mostly any Unix based computers and on Mac OS X.
# apt-get install vimOn ArchLinux based distibution, do the following.
# pacman -S vim
Note: if you want to learn the basics you can visit vim - Basics
You want to know more cool feature from vim have a look at my other vim tutorials.