Sinclair QDOS
Sinclair QDOS was the multitasking operating system found on the Sinclair QL and its clones.
Rewritten, enhanced versions exist in the form of Minerva, SMS2 and SMSQ/E. The latter being the most modern one which is still being improved.
Originally written for the Motorola 68000 CPU, with a 48k ROM for a computer with only 128k RAM.
Sinclair QDOS included the SuperBASIC interpreter, a well designed variant of BASIC with structured programming additions.