The best replacement for x plane is fsx.

The best alternatives to x plane are rated as following:
★★★★★  fsx
★★★  flight simulator
★★★  flightgear
★★  infinite flight
★★  flight sim x
★★  msfs
★★  prepar3d
★★  microsoft flight simulator
★  flight simulator x
★  p3d
★  ms flight simulator
★  fs2004
  microsoft flight sim
  flight sim
  fsx better

Your alternative for x plane is not listed? Suggest!
Speaking about x plane, one probably shouldn't forget about vatsim.

Other search terms related to x plane and their ratings are:
★★★★★ vatsim
You have in mind a companion for x plane and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of x plane in all years. Click on graph for more.
x plane
fsx
flight simulator