What is Ubuntu?
Ubuntu is a community developed, linux-based
operating system that is perfect for laptops,
desktops and servers.
It contains all the applications you need -
a web browser, presentation, document
and spreadsheet software, instant messaging
and much more.
Ubuntu Desktop Edition
Welcome to Kubuntu
Kubuntu is an official derivative of Ubuntu
using the KDE environment instead of GNOME.
It is part of the Ubuntu project and uses the same
underlying system.
It is an exciting distribution that showcases the full
potential of the KDE desktop. Kubuntu shares the
same repositories as Ubuntu, and relies on the same
underlying architecture.
Kubuntu Here
Welcome to Xubuntu
Xubuntu is a complete GNU/Linux basedoperating system with an Ubuntu base.
It is lighter on system requirements and tends to be
more efficient than Ubuntu with GNOME or KDE,
since it uses the Xfce Desktop environment, which
makes it ideal for old or low-end machines, thin-client
networks, or for those who would like to get more
performance out of their hardware.
xbuntu Here