(Other operating systems for the same hardware are the members of the MVS - OS/390 - Z/OS family.)
VM/CMS has two main components, VM and CMS, each an independent operating system. VM is a virtual machine system which provides each user with what seems to be their own personal mainframe; CMS is a relatively simple single-user operating system, designed to run principally under VM. Each VM/CMS user is given their own virtual machine to run CMS in.
Development started on what was then called the "CP-40 Project", working with a modified System 360 Model 40, at IBM's Cambridge Scientific Center (CSC) in the Fall of 1964. CP-40 was a virtual machine operating system; a simple interactive computing single-user operating system, CMS, was designed to go along with it. Actual implementation started in 1965, and the complete system was first available to users in early 1966.
VM/CMS was not started as a formal IBM product, and for many years there was a great deal of political infighting within IBM, over what resources should be available to it, as compared with competing IBM products.
After IBM announced the System 360 Model 67, the software was converted to run on that; CP-40 was renamed CP-67 at that point. An early version of the system was installed at MIT's Lincoln Labs in 1967, because of Lincoln's dissatisfaction with the "standard" IBM time-sharing offering, TSS (Time Sharing System), which was at that time very slow and unreliable. Lincoln personnel co-operated with CSC is improving the system; another influential IBM customer, Union Carbide, also decided to run VM/CMS, and also contributed to its development.
By early 1968, word had spread, and most System 360/67 sites were actually running VM/CMS, not the "official" IBM system for the machine, TSS. This eventually led to the demise of TSS, in 1971.
Thereafter, the utility of the system prevented all attempts to kill it, and IBM finally accepted the inevitable with relatively good grace, having learned through internal experience just how useful it was.
VM 370 Welcome screen :
VM/370 ONLINE
VV VV MM MM
VV VV MMM MMM
VV VV MMMM MMMM
VV VV MM MM MM MM
3333333333 777777777777MMMM 00000000
333333333333 77777777777 MM 0000000000
33 VV33 77VV 77 00MM 00
V33 VV 77M 00MM 00
33 VV 77MM 00MM 00
3333VV VV 77 MM 00MM 00
3333 VVVV 77 MM 00MM 00
33 VV 77 MM 00MM 00
33 77 00 00
33 33 77 00 00
333333333333 77 0000000000
3333333333 77 00000000
RUNNING