In short
The AETHER arcade cabinet was a Raspberry Pi 4 running a fullscreen Pac-Man-style HTML5 game controlled with an X-Arcade Trooper 2 joystick. It used a pi-build image like the other Pis in the show.
Connected to the show
High scores synchronized over MQTT. The game also reported when runs started and ended, including which ending a player reached. If the network was unavailable, the game still ran with a local scoreboard.