Xubuntu is a GNU/Linux distro.  If you don’t know what GNU/Linux is prepare to be very lost.

A friend wanted a CD of GNU/Linux to try out recently.  I burned them a copy of Xubuntu to try out.  Before I gave it to them I tried it myself by installing it on an old PC.  It was much faster than Ubuntu.  I am not saying that Ubuntu is bloated, just that it requres more to run.  I really like Xubuntu because it is much faster.  It does not include fancy transitions when you alt-tab to other applications like Vista or Ubuntu.  Although you can disable those fancy transitions.   Xubuntu does seem somewhat like Ubuntu for Apple people.  More Mac keyboard shortcuts seemed to work than Ubuntu.  I like Xubuntu a lot and it has replaced Ubuntu for me.