The MenuetOS (or MeOS) operating system (OS) has a monolithic, preemptive, realtime kernel, including video drivers, for 32-bit and 64-bit x86 architecture computers. It has a graphic desktop, games, and networking (TCP/IP stack), yet fits on one 1.44MB floppy disk.
Development focuses on being fast, simple, efficient. It is all written in FASM Assembly language, and facilitates easy, full-featured Assembly programming, in contrast to the common view that Assembly languages are usable mainly for old and embedded systems.
MenuetOS was originally written for 32-bit x86 processors and released under the GPL, so many of its programs are licensed as GPL. The 64-bit MenuetOS, often called Menuet 64, remains a platform for learning 64-bit assembly language programming. Menuet 64 is distributed as freeware with no source code for core components. It works smoothly in QEMU which can emulate a 64-bit machine on a 32-bit machine. The author is Ville Mikael Turjanmaa.
KolibriOS is an operating system (OS) for x86 PCs. It was originally a MenuetOS distribution, with some improvements, by a Russian developer team. It has now become a MenuetOS fork project, by the KolibriOS Team. Both OSs are written in the Assembly programming language FASM. But C, Free Pascal, and Forth can be used for user programs. KolibriOS has a GNU General Public License, so it is free, open source software.