The term for multiple displays is "Dual or multi-head"
The term for multiple, independent users is "Multiseat"
Those should get you somewhere near the entrance to the rabbit hole. Enjoy your journey.
The view and interact part, when I explored this stuff, is very insecure by today's standards. Can be fun though. :D
> Want to make a computer that several people use locally, each with their own screen, keyboard, mouse? X can do that, and permit those users to view and interact with any combination of each others display data.
> One says, hey can you sort this for me? Another says, "sure", and a window pops up on their screen...
Is there literature or something about setting up complex things like this in X? I'd be interested in learning more.