  Unmanned aerial systems capable of beyond visual line of sight operation can
be organized into a top-down hierarchy of layers including flight supervision,
command and control, simulation of systems, operating systems, and physical
hardware. Flight supervision includes unmanned air traffic management, flight
planning, authorization, and remote identification. Command and control ensure
drones can be piloted safely. Simulation of systems concerns how drones may
react to different environments and how changing conditions and information
provide input to a piloting system. Electronic hardware controlling drone
operation is typically accessed using an operating system. Each layer in the
hierarchy has an ecosystem of open-source solutions. In this brief survey we
describe representative open-source examples for each level of the hierarchy.
