The Alien package converter is a handy little tool to have around when you’re dealing with developers who cater to specific distribution packages.
With a simple command, Alien will convert Debian, Slackware or RPM packages from their native format into one of the others for ease of installation on the given distribution. It cautions you to beware some packages, as Red Hat and other distros have a habit of putting things in non-standard locations, but with most packages the user should be in good shape.
It’s based on Perl, and if you want to handle RPM or Debian package you’ll need the appropriate package manager installed on your system. Of course, at that point you might be thinking “why mess with conversions?”
Simple: distribution. You may not have much use for it on your own system, but it’s great for sharing packages with friends and family or for distributing software you may develop to end users.