I'm fond of early video image grabbers -- both single frame and continuous. They challenged what it was possible to do with a Mac II family computer.
Wow, a Disk ][ controller for NuBus Macs. When the hard disk runs out of space on the old 840/AV, just imagine how useful that extra 140KB of storage is going to be ;-) BTW, how do you load cassettes on a Mac II?Anyway, I know it's as common as shit, but I'd say the Disk ][ controller card. Life with casette tapes is a pain after all.