WAG ... Fortran.
Close! The Intellec Microcomputer Development Systems (MDS) were complete computers intended for the development of Intel microcomputer based products and ran an operating system callee ISIS. But, one of the languages supported by ISIS was FORTRAN, as well as PL/M. Having sweated over one of these back in the 70s, it’s still the first thing I think of when I see ISIS!
But what’s in a name ;-)