os8088 boots from the first sector of a floppy into a graphical desktop. There is no DOS underneath it and no command line anywhere in it -- the 512-byte boot sector loads a 40KB kernel, the kernel works out which display adapter the machine has and switches it into graphics, borrows the video card's own 8x8 character set, and puts up a menu bar.

Everything after that is the interface you remember from a 1984 Macintosh: windows you drag by the title bar with a rubber-band outline, menus you pull down and drag through, a close box and a minimize box, icons for each floppy drive, and a dock along the bottom with one tile per running program. Programs load from a second floppy and run as first-class applications, several at a time.

The whole thing fits in 256K of RAM on an Intel 8086 or 8088 -- the processor in the original IBM PC and PC/XT. It is a hobby project, it is finished enough to use, and the source is 66,183 lines of NASM you can read in an afternoon.