ardupilot

ArduPilot is the autopilot software behind over a million drones, rovers, boats, and submarines. The entire stack is GPLv3, no paid tiers, no cloud lock-in. You flash it onto a Pixhawk flight controller and get GPS navigation, mission planning, autonomous waypoints, return-to-home, and failsafe handling out of the box. NASA, Boeing, and Intel all use it in production vehicles.

Running ArduPilot means running real hardware. You pick a flight controller (Pixhawk is the standard), flash the firmware, calibrate sensors, and configure your vehicle type. The toolchain is C++ and Python. Ground control stations like Mission Planner or QGroundControl handle the UI side. Expect a weekend to get your first vehicle flying reliably, longer if you're building custom frames.

Solo hobbyists and university research labs get everything for free. Commercial drone operators use it to avoid DJI's ecosystem lock-in. Large teams building autonomous fleets use ArduPilot as the base layer and add their own control software on top.

The catch: this is aerospace firmware, not a web app. Misconfiguration can crash a physical vehicle. The GPLv3 license means any firmware derivative must also be open source, which some commercial OEMs avoid.