One of
IBM's early
mainframe families, released in the mid-sixties, replacing all earlier systems. OS/360, the operating system, was notable for being portable across a wide range of models.
IBM was motivated to create a universal operating system for it's hardware to reduce application software development costs, which were steadily increasing relative to hardware. It also provided an easier upgrade path for customers.
The development of System/360 was the largest software development project in history at the time. Frederick P. Brooks headed the project, and revealed many insights learned on the project in his well-known book, "The Mythical Man-Month".