FreeDOS
From OS-Tan Collections Wiki
FreeDOS is a free (/libre/opensource) implementation of MS-DOS. It works for most applications and has reached version 1.0 lately.
FreeDOS-tan is a shy creature, who likes to peek around corners due to her occurance in embedded systems. Her design looks similar to MS-DOS's, but her hair is brightly blue, she has GNU-horns and wears a necklace with a fish, as reference to FreeDOS's mascot. Like all DOS-tans, she has a flat chest and not much appetite.