A device that works at the application layer is typically known as what?

A device that operates at the application layer is typically referred to as a gateway. Gateways facilitate communication between different networks and often translate protocols, enabling systems that use different protocols to communicate effectively. They act as a "gate" between two networks and can manage data based on application-level protocols, making them integral in providing services that require higher-level processing of data.

In contrast, routers primarily function at the network layer by directing data packets between networks, while bridges operate at the data link layer to filter traffic and strengthen connections between LAN segments. Repeaters are focused at the physical layer, amplifying and regenerating signals in order to extend the range of communication. Thus, a gateway stands out as the correct answer, as it specifically engages with application-level interactions, making it distinct from the other devices mentioned.