ArduPilot/ardupilot ? reverse-engineered prompt

Build me a serious open source autopilot firmware project for unmanned vehicles. I want one shared codebase that supports multiple vehicle types, especially copters, planes, rovers, subs, and an antenna tracker, with vehicle specific code on top of common libraries.

The software should feel reliable and full featured, with the basics people expect like stabilization, navigation, waypoint missions, GPS and sensor handling, telemetry friendly communication, and logging. It should be possible to build and run each main vehicle type in a local software simulation so I can test things without real hardware first.

Please make the project easy to build, easy to test, and organized like a long running community robotics project. Include practical docs for setup, building, running the simulator targets, and where the main vehicle code lives. Add automated tests where appropriate so the main targets keep working.

If you need exact behavior or setup details, look up the current ArduPilot docs online and match that experience as closely as you can.