The majority of the flight simmers uses a version based on the original from Microsoft. These are FS9, FSX, FSX-SE and Prepar3D which I use myself. The FSX versions (FSX-SE possibly excepted) are (very) ancient products and Prepar3D is (fortunately) a development long waited for that is satisfying. Besides these products there is also something called X-Plane. This is a product from Laminar Research (Austin Myers) and the installed base is ever growing. X-Plane has a number of advantagfes over the Microsoft based products and ofcourse also some disadvantages. Reasons enough to check things out.