Plug-in development
From X-Plane Wiki
Plug-ins are extensions to X-Plane that add features and functionality not included in the released version of the simulator. Plug-ins can be used to provide alternatives for built-in features of the application (e.g. a replacement autopilot) or to provide new features (e.g. a plug-in to enable flying online). Plug-ins are written in C or C++, but several plug-ins have been written that 'wrap' other languages, enabling script-based plugins to be developed.
Developing Plugins
Binary Plugins written in C / C++ are developed using the X-Plane Plugin SDK which is maintained by Sandy Barbour. The plugin SDK is a separate project from X-Plane and v2.0 has been released in conjunction with X-Plane v9.0.
Other Languages
Wrappers for the following languages have been developed: