Refer: http://en.wikipedia.org/wiki/List_of_Linux_distributions
Distributions are organized into sections by the major distribution they are based on, or the package management system they are based around

cat /etc/debian_version

• Debian GNU/Linux is a distribution that emphasizes free software. It supports many hardware platforms.
• Debian and distributions based on it use the .deb package format[1] and the dpkg package manager and its frontends

• Knoppix: The first Live CD (later DVD) version of Debian GNU/Linux
• Ubuntu: A distribution sponsored by Canonical Ltd. and receiving major funding from South African Mark Shuttleworth. Aims to offer a complete and polished desktop on a single DVD

• Kubuntu: An official derivative of Ubuntu using KDE instead of the GNOME or Unity interfaces used by default in Ubuntu
• Ubuntu for Android: Designed for use with Android phones
• Ubuntu GNOME: An official Ubuntu variant[59] that uses Gnome Shell as its default desktop and GDM as its display manager.
• Ubuntu Server: An official derivative made for use in servers. Ubuntu Server handles mail, controls printers, acts as a fileserver, can host LAMP and more
• BackTrack: Developed by Offensive Security and designed for penetration testing.

Red Hat Linux and SUSE Linux were the original major distributions that used the RPM file format, which is today used in several package management systems. Both of these later divided into commercial and community-supported distributions:

• Red Hat Linux divided into a community-supported distribution sponsored by Red Hat called Fedora
• and a commercially supported distribution called Red Hat Enterprise Linux

• Atomix: a Serbian desktop and server oriented Linux distribution
• Network Security Toolkit: A Live CD/DVD with security and networking tools to perform routine security and networking diagnostic and monitoring tasks
• Trustix: A distribution focused on security

• CentOS: Community-supported distribution that aims to be compatible with Red Hat Enterprise Linux without the inclusion of proprietary software
• ClearOS: Small Business Server. File, Print, Messaging, UTM, VPN.
• TrixBox: A Voice Over IP (VoIP) distribution based on CentOS.