Though it can do other stuff, I use this to edit ISO images meant to be burned to a CD or DVD, to make them appropriate for copying to, and booting from, a USB stick.
Phenomenal. I wish I knew about this a long time ago. I've ignored many Linux distributions because of the very issue this tool solves.
A bootloader with various companion tools.
Seems fantastic, but only in the sense that various other tools use it in magical automated ways.