100% 64bit assembly OS MenuetOS (opens in new tab)

- Pre-emptive multitasking with 1000hz scheduler, multiprocessor, multithreading, ring-3 protection

- Responsive GUI with resolutions up to 1920x1080, 16 million colours

- Free-form, transparent and skinnable application windows, drag'n drop

- SMP multiprocessor support with up to 32 cpus

- Time critical process support: an uninterrupted process execution on any cpu

- Kernel/user mode pre-empting, including SMP

- Up to 100000 hz process scheduler, below millisecond audio latency

- IDE Editor/Assembler for applications

- USB 2.0 Classes: Storage, Printer, Webcam Video and TV/Radio support

- USB 1.1 Keyboard and Mouse support

- TCP/IP stack with Loopback & Ethernet drivers

- Email/ftp/http/chess clients and ftp/mp3/http servers

- Hard real-time data fetch

- Fits on a single floppy, boots also from CD and USB drives

Ah is this still going, i tried it i think like 10y ago, was only 1,4mb then and quite impressive fot that size!