KeyKOS

KeyKOS is a persistent, pure capability-based Capability-based [operating system|operating system] for the IBM S/370 mainframe computers. It allows emulating the environments of VM, MVS, and Portable Operating System Interface. It is a predecessor of the Extremely Reliable Operating System, and its successor operating systems, CapROS, and Coyotos. KeyKOS is a nanokernel-based operating system.
In the mid-1970s, development of KeyKOS began at Tymshare, Inc., under the name GNOSIS. In 1984, McDonnell Douglas bought Tymshare. A year later MD spun off Key Logic, which bought GNOSIS and renamed it KeyKOS.