An Automated Transfer Vehicle, also known as ATV is a payload which has 8 cargo slots (compared with Apollo's 3, Orion's 5, and the Resupply Module's 6). Since it has integrated solar panels, none of these cargo slots need to be occupied by a battery.
While real-life ATVs can dock with the space station automatically, the ATV in Space Agency must be piloted manually. It is also pressurized.
The ATV is unique among spacecraft (not station modules) in that it has docking ports on both sides. This allows a long string of them to be docked together while each of them still retaining the main engine's functionality. This also allows for placing the ATV in the middle of a large Station which makes it able to retain of sideways motion without any pitch change.
It is perfect for space exploration, and the main engine's restart has no latency unlike other vehicles like Station Builder Tug, Resupply Module or Apollo Service Module allowing for precise and accurate movements. Only the Tug Module and LOK Service share this ability with the ATV.