MenuetOS (also known as MeOS) is an operating system with a monolithic preemptive, real-time kernel, including video drivers, all written in FASM assembly language, for 64-bit and 32-bit x86 architecture computers, by Ville Mikael Turjanmaa.

MenuetOS development has focused on fast, simple, efficient implementation. It has a graphical desktop, games, and networking abilities (TCP/IP stack), yet it still fits on one 1.44MB floppy disk. It also facilitates easy, full-featured assembly language programming. This stands in marked contrast to the (as of 2009) widespread view that assembly languages are useful mainly for old and embedded systems.[citation needed]

MenuetOS was originally written for 32-bit x86 architectures and released under the GPL, thus many of its applications are distributed under the GPL. The 64-bit MenuetOS, often referred to as Menuet 64, remains a platform for learning 64-bit assembly language programming. 64-bit Menuet is distributed as freeware without the source code for core components. Menuet 64 works smoothly in QEMU which can emulate 64-bit machine atop a 32-bit machine.