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