We've all at least heard of KSP, a popular space flight simulator. its not the best but can teach someone the basics at rocket science, delta V, burntime, basic orbital maneuvers, retrograde, prograde, etc. but we all know its also not very accurate, because of how it has on rails and physics simulations at once.
by accurate i mean most similar to real life ex: in KSP atmospheric drag just cuts off in this more accurate simulation it is a long gradient.
My question is what simulations are more accurate at simulation?