FreeDOS

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. FreeDOS can be booted from a floppy disk or USB flash drive. It is designed to run well under virtualization or x86 emulation. Unlike most versions of MS-DOS, FreeDOS is composed of free and open-source software, licensed under the terms of the GNU General Public License. Therefore, its base distribution does not require license fees or royalties and creation of custom distributions is permitted.