A variant of CP/M which was designed by Digital Research for use with the Intel 8086 microprocessor and compatible with the later Intel 8088. It followed CP/M as IBM's preferred operating system for the IBM PC.
However, it faded out of use primarily because Digital Research and IBM could not agree on contract licensing and fees. IBM then took up with Bill Gates and Microsoft to use MS-DOS.
This was what set in motion Microsoft as an operating system provider and was ultimately the demise of compact and manageable operating systems for Personal Computers until Microsoft's grasp on them was loosened somewhat. So, ultimately, part of the blame can be laid at the feet of IBM.