Fonts from one machine
Window management from another
An application running on yet another, with it's program data sourced from yet another machine accessing data on still another machine.
All of which is displayed on another machine also supplying user input.
Or, I could do something crazy like put a window on your display, with appropriate permission of course, and you could interact with it.
A big wall type display could take windows from a number of users.
The promise back then, and something I used a lot, an many still do use today, is being able to run something and display it somewhere else. Say my cellphone is on my desk. I could ask it to do something for me, and the window into that activity appears on the display like any other window does.
Another case might be several users running on one machine each with their own displays and inputs.
Here is a real world case:
High end CAD software, managed data, many users.
With X, one can make a big application server and that is not visible to users at all in terms of the application or data to be manipulated.
Users run the program via X, running X servers on anything they want. PC, Mac, Linux, whatever.
The only way to interact with the managed data is through the application.
One copy of the application, one data repository, many users.
With X doing that kind of thing is easy, and it works whether one user runs the app on their local machine attached to a shared data repository, or many users run on a remote machine perhaps that machine itself also holding the data repository.
All of that is extremely possible with a web app though, and most of it is probably done even easier with a web app. In fact that is the usual way to build a web app, make a server that does the heavy lifting and then make a GUI that runs in the client which can then be accessed by multiple users. You can easily access them from a smartphone too.
The only exception is this:
"Another case might be several users running on one machine each with their own displays and inputs."
This would be multi-seat which doesn't really have anything to do with the display server. It is implemented in udev and logind, which spawns additional X or Wayland servers for each additional "seat".
Is that sarcasm? A key difference I would say is that the web is actually better because you can run javascript or WASM code in the browser, in X that would be the equivalent of the "server"...
Fonts from one machine Window management from another An application running on yet another, with it's program data sourced from yet another machine accessing data on still another machine. All of which is displayed on another machine also supplying user input.
Or, I could do something crazy like put a window on your display, with appropriate permission of course, and you could interact with it.
A big wall type display could take windows from a number of users.
The promise back then, and something I used a lot, an many still do use today, is being able to run something and display it somewhere else. Say my cellphone is on my desk. I could ask it to do something for me, and the window into that activity appears on the display like any other window does.
Another case might be several users running on one machine each with their own displays and inputs.
Here is a real world case:
High end CAD software, managed data, many users.
With X, one can make a big application server and that is not visible to users at all in terms of the application or data to be manipulated.
Users run the program via X, running X servers on anything they want. PC, Mac, Linux, whatever.
The only way to interact with the managed data is through the application.
One copy of the application, one data repository, many users.
With X doing that kind of thing is easy, and it works whether one user runs the app on their local machine attached to a shared data repository, or many users run on a remote machine perhaps that machine itself also holding the data repository.