Is there any more text under the blue capacitor at the bottom? A][ ????? What does it say at the top? Are there any hidden letters? That might hint at Apple ][ (what). It's a dual port parallel interface to something, perhaps a printer, depending on the firmware. What happens when you address it, ie put it in a slot and type "PR#(slot)" and "IN#(slot)"? You may have to disassemble the ROM code to figure out what it's for. It doesn't seem likely to be for a floppy unless the floppy has onboard intelligence. It might be for an IDE HD, but then the cable would probably be 40 pins. If SCSI, it would have 50 pins. 6821s were often used for printer interface cards. The RAM would be for buffering text so the printer could work while the Apple went about another task.