KeyKOS is a persistent, pure capability-based operating system for the IBM S/370 mainframe computers. It allows emulating the VM, MVS, and POSIX environments. It is a predecessor of the Extremely Reliable Operating System (EROS), and its successors, the CapROS and Coyotos operating systems. KeyKOS is a nanokernel-based operating system.
The development of KeyKOS started under the name GNOSIS in Tymshare, Inc. during the 1970s and continued under the name KeyKOS after being bought by Key Logic.
References
KeyKOS Wikipedia(Text) CC BY-SA