An application to operate a fleet of drones delivering goods:

The command center sends an instruction to the drone to pickup an item from the warehouse (only one at present).

The drone picks up the item from a designated spot (one spot only at this moment) and lifts off to the delivery address.

After it reaches the delivery address, the drone sends an instruction back to the command center that it has reached.

The drone unloads the item and sends an instruction back to the command center that it has unloaded the item.

It comes back to the warehouse, reaches its parking spot, and lets the command center know that it is ready for next instruction.