Penetration Testing System
A penetration test distribution should run from a LiveCD and include all the tools needed to analyze the system for any potential vulnerabilities. The user must have the tools needed to simulate the hacking of the system from an outside source with no actual knowledge of the system and a report with recommendations should be generated once the pentest is complete.
Backtrack, Operator and Knoppix-STD are all examples of Linux distributions designed for the sole purpose of penetration testing. They include, on the LiveCD, hundreds of security tools to aid you in your penetration testing. Each boots from a LiveCD and runs entirely in RAM.
System with a Small Footprint
A system designed with a small footprint as its goal should attempt to keep the size small but not sacrifice usability for size. These distributions should be able to boot from a business card size CD (staying under 100MB) as a LiveCD. It should load the entire OS into RAM to free up the CD drive for other uses and provide the user with a full range of applications. There should be an option to install the distribution to your hard drive as well as the ability to save all user files and preferences to hard drive (or usb key) if running from the LiveCD.
Puppy Linux and DSL (Damn Small Linux) both do an excellent job of keeping the distributions size small while offering the user a full range of basic applications. Both run entirely from memory and the performance of each distribution, on a wide range of hardware, is exceptional. Both are useful for OS troubleshooting, file recovery following a hard drive crash, or as a fully functional personal OS. One great thing about these two Linux distributions is that you can install them to a usb key and take them anywhere you go. Very cool!
Linux: The Choices are Endless
This article covers only a fraction of the custom Linux distributions out there. We have Linux distributions designed for education (Edubuntu), Gobuntu and gNewSense, all based on Ubuntu and consisting of entirely free software, and even the now defunct Ubuntu CE (Christian Edition) that catered to christians.
As you can see the choices are indeed endless with Linux! There are literally hundreds of distributions out there catering to a wide range of specific users. That being said, this is Linux we are talking about, if you can't find a distribution that meets your needs ... build one yourself!