Don't forget MUSIC/SP
MUSIC/SP - Multi User System for Interactive Computing, brainchilded at McGill University was an exceptional late 70's - early 80's multi-user Operating System which also ran under VM (or autonomously) allowing hundreds of simultaneous users in the resource space of just a few CMS users.
While not really a virtualization system itself, it gave the end-user the impression that they were working on their own interactive "machine".
TSS (and later the premier transaction processing system in the world, CICS - Customer Information Control System) also provided (provide) multi-user environments which give the user impression of one's own machine, but not really virtualization, per se.
The combination of VM/370 and MUSIC/SP ended up being one of the most dynamic, efficient, cost-effective, amazing and user-friendly multi-user environments that IBM has ever produced.
Thanks for the walk down memory lane.
BTW, was not PR/SM really just a specialty version of VM?