As a warm up:
With all that setting the scene done, let’s get down to how I wrote an 88-byte 8086 bare-metal mandelbrot generator.
And here’s Óscar Toledo G’s BootOS:
bootOS is a monolithic operating system that fits in one boot sector. It’s able to load, execute, and save programs. Also keeps a filesystem. It can work with any floppy disk size starting at 180K.
[Side note; the Familia Toledo are performing a ground-up computing crusade. Here’s their $99 computer with homegrown OS and web browser.]
Oh, and it seems there was an annual contest for 512 byte operating systems.