YUMI Multiboot USB Creator
Yumi, short for Your Universal Multiboot Installer. YUMI allow you to prepare the bootable USB drive multiple operating system in one USB drive without formatting it.
You can download the ISO of your favorite OS. YUMI have large collection of free OS based on Linux and other free OS projects. Just select what you want and YUMI will give you the direct download link for it.
The inrface is quite easy to use and useful.