Tip Monkies decided to help Linux newbies by comparing all the major Linux distributions with each other. Here's a short snip from the article:
There are two major trunks for most Linux distros. There are plenty of ground up distros, but most are derived either from RedHat using RPMs (RPM stands for RedHat Package Manager) or Debian using dpkg files. This file formats are used to install software on your computer. Currently, the biggest distros not derived from RedHat or Debian are Slackware and Gentoo which also have their own package management systems with various advantages/disadvantages.