Wikipedia
FlexOS
FlexOS was a modular real-time multi-user multi-tasking operating system ( RTOS) designed for computer-integrated manufacturing, laboratory, retail and financial markets. It was developed by Digital Research's Flexible Automation Business Unit in Monterey, California since 1986 and was marketed since January 1987 as a reengineered derivation of Digital Research's Concurrent DOS 286 multiuser multitasking operating system.