Welcome to Gaia! ::

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Method I
apt-get
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Debian and most Debian Based Systems including Ubuntu have a command line installer (Which the GUI installers also use) that can be executed from the terminal (xterm, konsole) so you can install apps from Repositorys without the GUI slowing you down. The command used in these systems is
which will show you what commands ect you could put after it to run the program. The main use of this if you already know the name of the package would be

Replacing kde with the package you wish to install
Just Like a GUI installer it will find and install all the applications it needs for the package you are installing
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Method II
aptitude
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apititude is CLI (Command Line Interface) program with a GUI that can be run from a terminal and contains the same list as a GUI based installer in Gnome or Kde which may become useful if you can't (or don't want to) start your X server but still want to be able to install from a list.
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Comment on how to improve this biggrin

I've recently only been using Ubuntu (8.10) on my laptop I bought recently. On my older Desktop (hardly ever use doesn't even have a mouse attached to it mainly alarm clock XD)I've been running Debian (etch) / OpenSUSE (10.3) so all I've recently used is APT and Yast
I'm open to anyone's knowledge that could make the post cover more package managers