FIrstly - a great New Year to all!
I don't think I mean stuff like military aircraft carrier training or something Boeing uses at their factory, (but if you have experienced any of that, then do tell)
After an earlier casual effort, I am just about getting started trying FlightGear more seriously. So..
X-Plane - a paid-for sim which the developers claim is not a game. Using something called "blade element theory", which is "an engineering tool that can be used to predict the flying qualities of fixed- and rotary-wing aircraft with incredible accuracy.” Is that a bit like JSBSim?
YSFlight - I don't know anything about it, other than it does not require much computer power to work OK.
Google Earth Flight Simulator - so far, no way could it see the joystick on my Linux machine. No doubt it needs "drivers". I am not even sure the mouse worked OK with it properly, but for me, however great is the photographically derived scenery, a top wide-angle view, transformed to pretend a tilt for viewer eye position, delivers all the wrong motion cues compared to a proper 3D perspective transform of even sparse airport objects.
Microsoft's Flight Simulator - Where the original Cessna 172 became familiar to us all, and once used by some as a casual MSDOS functional test. It is no longer with us, and may have been developed for professional use by companies like Lockheed Martin. It may not have much relevance to our community now, but one can hardly not mention it!
https://en.wikipedia.org/wiki/Microsoft_Flight_Simulator
Condor This is a paid-for "Competition Soaring Simulator", meaning sailplanes .. gliders.
This one keeps the focus on claimed "high accuracy aerodynamics and weather physics". They leave the scenery to what looks like Google Earth derived, though I am not sure.
This is one I have had the opportunity to try out while sat in a full-size glider fuselage mock-up in a room with 3 projector monitors pointed at the walls of a room. All driven off a regular PC with a couple of graphics cards. The messed perspective when trying to judge whether one has flown far enough to do a base leg and final turn was alarming, and just plain unrealistic! That said, the whole aero-tow experience, including encountering the propeller wash, various thermal lifts, incipient spin when overdoing the rudder while going too slow, all of these seemed good, though I would only be able to compare if I got to try out the real aircraft. I guess perhaps too specialist for those who want full airliner flying with engines. Not for me because it runs on various Microsoft Windows, and my PC is a Linux box.
There are bound to be others..