I was thinking that it is possible to use PureBasic - which produces FASM .asm files as intermediate - to have some comfortable high-level environment to build applications for MenuetOS... But many wanted benefits are not kept (e.g. dimensioning an array calls an external subroutine - it is not translated into assembly). From string manipulation to hashmaps, a library should be built to comfortably code for MenuetOS.
Edit: KolibriOS seems to document more options ( http://diamond.kolibrios.org/hll/hll_eng.htm )