MultiBoot USB
This is a collection of GRUB scripts that allows to create a bootable pendrive (USB dongle, flash stick) supporting a number of different OS images. Simply copy ISO files under `/iso-imgs`. Both UEFI and Legacy BIOS boot modes can be enabled simultaneously.
FreeDOS (formerly Free-DOS and PD-DOS) is a free operating system for IBM PC compatible computers. It intends to provide a complete DOS-compatible environment for running legacy software and supporting embedded systems.