Slax

SLAX is fast and beautiful Linux operating system. It runs directly from the CD (or USB) without installing. The Live CD described here is based on the Slackware Linux distribution and uses Unification File System (also known as unionfs), allowing read-only filesystem to behave as a writable one, saving all changes to memory.
Minimum Hardware Requirements
SLAX is not pretentious, nevertheless it requires some minimal hardware to run properly. It depends on what do you wish to use SLAX for, of course. The most important thing is memory. You need at least 32 MB of RAM to boot Slax.

Slax is a Slackware-based bootable CD containing a Linux operating system, designed with a modular approach. Despite its small size, Slax provides a wide collection of pre-installed software for daily use, including a well-organised graphical user interface and useful recovery tools for system administrators.