Microsoft Flight Sim - not much more than a toy in most respects, but very useful for IMC stuff.
The biggest problem with MSFS - and this will apply to any PC-based simulator - is the feedback from the controls. At work we've got a professional yoke and rudder pedals, with a trim wheel which provides force through the control column, so it's a far more realistic feel than the joystick you've probably got at home, but it's absolutely nothing like a real aeroplane. But a great tool which I use with some of my IMC students, particular when they're struggling to understand something, and if you've got a rating but just want to keep in practice without paying for a real aircraft it'll certainly get your scan going.
FFF
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