Source: http://menuetos.net/MenuetOS is an Operating System in development for the PC written entirely in 32/64 bit assembly language. Menuet64 is released under License and Menuet32 under GPL. Menuet supports 32/64 bit x86 assembly programming for smaller, faster and less resource hungry applications.
I found the platform in an interesting Norwegian (use a translation service) forum thread about assembly:
How to start in Assembly?