AD1 ROM Cartridge
The AD1 ROM Cartridge from Arnor is a miniature ROM board that accepts only one single ROM/EPROM chip. It was (optionally) shipped togther with Arnor ROM software (namely with MAXAM and Protext; maybe it was also used for other ROMs).
The purpose was to motivate people to buy ROM software, without forcing them to purchase more expensive multi-socket ROM boards.
There is also an AD2 version, which is expandable to hold 4 ROMs.