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.

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.