Their site indicaters it is a fork ? or menuetOS (Meos)http://wemakeitbig.com/meos/
The 64-bit main distribution is now proprietary. Several distributions of the 32-bit GPL MenuetOS still exist, including translations in Russian, Chinese, Czech, and Serbian. Menuet64
It would be useful, as it is a fork, if they would indicate the difference between their version and MenuetOS: if any ?
About KolibriOS from Kalibri Wiki :
KolibriOS is an open source operating system with a monolithic preemptive kernel, video drivers, for 32-bit x86 architecture computers, developed and maintained by The KolibriOS Project Team. KolibriOS is a fork of MenuetOS, written entirely in FASM (assembly language).
But, something like Puppy which runs fairly quickly from RAM, and is fairly small, is possibly more useful, unless you happen to need a very small OS as a diagnostic system
--it would lack the desktop experience we are all used to with most of the Linux distributions available (large or small on CD or DVD) or otherwise, USB sticks (business card OS)..