I work for NATS (National Air Traffic Services, although we're not supposed to call it that any more, "branding" and all that ). We do air traffic control simulations. They are used to train new air traffic controllers and try new stuff out before it gets implemented for real. For example new tools that predict the trajectory of aircraft in the medium term to sort out potential conflicts and enable the controller to handle more traffic - they were all simulated by us.
Some of our sims have 30 odd controller positions, each of which has 2 radar displays and a couple of information displays. Then there are >30 pilot positions where guys basically pretend to be the aircraft. Behind it all there is a pretty complex model that simulates the aircraft performance etc, and how they would appear on radar etc. All that lot is basically one big distributed system.
No flight sims though, sorry!