Debian is a lightweight, stable, and mature linux distribution that has been around since 1993 and has over 29,000 software packages. The package design is quite modular, which allows developers to pick exactly what is needed for their project without building everything from source.
2 Package Management
Debian will offer [better documentation on this subject], but this should be enough to get started.
apt-get update apt-get upgrade
apt-get update apt-get install python2.4
apt-get remove python2.4
Search for packages
apt-cache search nmap