X-Plane is a very capable flight simulator on the Mac. It has a superior flight model to MS Flight Sim, which is based on generic aircraft. In X-Plane, it uses "blade element theory" to model the flow of the air over the wings. Thus, every aircraft has different flying characteristics (as you would hope). It is best explained on the
website. It will even show the lift vectors on the wings.
Scenery-wise, X-Plane was always the poor relation to the "eye candy" of MS Flight Sim. However, no more! If you purchase (all 60Gb!) of the
Global Scenerypack, you get a stunning array of scenery.
"Real" ATC can be provided to X-Plane over the
Vatsim network via a the
XSquawkbox plugin. You can communicate with virtual ATC using text or using a microphone. Some of the "controllers" can get quite baity if you don't adhere to the route.
There is an increasingly active XPlane community, most visible at
x-plane.org.
X-Plane is perhaps more for the purist. It more accurately models the flight dynamics of aircraft, from some crazy "original concept" designs to the usual Boeing and Airbus ranges. Being able to design your own aircraft means that you could, for example, put a glass cockpit into a Concorde, for example (heresy to some, I know)!
X-Plane is so flexible, that it can also model the atmosphere on Mars, and there are aircraft supplied with it (and available for download online) which are optimised for Martian flight. Landing with 400kts+ groundspeed is pretty thrilling. At a more terrestial scale, it is also possible to fly the shuttle re-entry in X-Plane.
The main differences between X-Plane and MS Flight Sim are those of the aerodynamic modelling and the concept of the application. MS Flight Sim is more aimed at "game players", whereby it offers "missions" and concentrates heavily on the visuals. X-Plane doesn't offer "missions", but leaves the field wide open to create your own.
Austin Meyer, who writes X-Plane is constantly upgrading the software, and barely a week passes before there is another beta available to test. Austin is also a
pilot himself, and there is great attention to detail.
I've been using X-Plane for several years now, and often download the betas. It's a very good tool for instrument practice, and I'm convinced it helped during my IR training.
For those with PCs, it works on those, too!