Austin Meyer, creator of the X-Plane flight simulator made an announcement recently on his website regarding the closure of the ACES studio by Microsoft:
X-Plane has become a real world-class flight simulation platform and with the SDK it is a great choice for cockpit builders. I’m a user of X-Plane and I’ve written plug-ins for it. I would highly recommend this if you’re looking for a commercial alternative to Microsoft Flight Simulator. For those that are interested in an Open Source flight simulator, you cannot beat FlightGear
I should also mention that X-Plane is cross-platform. It’s available for Windows, Linux and Macintosh.