If you go to distrowatch.com and look down the rankings you will see at number 24 a distribution called SLAX.
It is very hard for distro developers to make their particular distribution stand out. SLAX is not one of them.
SLAX weighs in at 210mb and is built to run from a USB drive as opposed to being installed to the hard drive. What you end up with is a fully functional portable operating system.
To download SLAX go to http://www.slax.org/en/download.php and click on the 32-bit or 64-bit zip file for your particular language.
Now ordinarily when downloading Linux distributions you would download the ISO image and burn it to the USB drive using something like UNetbootin but to install SLAX all you need is a USB drive, the zip file and a program that can extract the zip file to the USB drive.
rest here