This site is being deprecated.
Please see the official X‑Plane Support page for help.
You can install both PC and Mac. The key will allow you to download, install, and use X-Plane only on one computer at a time. For running both PC and Mac instances of X-Plane you should buy another licence key.
X-Plane for mobile devices is free. You can read more about it here.
This site is no longer being actively maintained.