Bets are good that if there's isn't a definite company logo or name and version number somewhere, it's probably the work of a hobbyist, someone with nice tools and equipment, maybe a kit maker as you suggested. There's a bunch of easily identifiable integrated circuits and they are:
MC68B21P - Peripheral Interface Adapter
HM6116LP-3 - 16K SRAM
NEC D2716D - 16K EPROM
74LS00 - NAND Gate (Logic)
74LS08 - AND Gate (Logic)
SN74LS38N (4) - NAND Buffer (Logic?)
74LS244 PC - Octal Driver Tri-State
74LS245 PC (2) - Octal Bus Transceiver Tri-State
74???? PC (1) - Not sure, seems to have lost it's markings to time (or a dark photo location)
Conclusion:
So, I think it's completely reasonable to consider an interface card, given the info. It would seem that it is an 8-bit interface since it uses an octal driver and transceiver. The fact that it has a transceiver suggests that it does input and output, not just one or the other. I would guess that it has firmware of some kind (given the EPROM), so it's not completely done in hardware. If it came with that cable it's probably not a Serial/Parallel card (can't say for certain) which means it's most likely not an input only device or a communications card. That said, I'd bet on some kind of storage interface, probably a floppy or hard drive interface. Although it maybe difficult to tell without testing.
If you're fairly sure it's for one of the Apple II series, you should get some specs on the Apple II bus and the circuitry. Then you should do some mental tracing backwards and get an idea of which connectors on the header go to positive voltage, ground, and data lines. Make sure that the circuitry (the ICs present) is actually rated for the Apple II bus interface voltages. If the results of a thorough examination line up with the Apple II bus specs, you can try plugging it in and see what happens. Even if it does connect to a PC floppy drive (which might be hard to say for certain), it probably won't work right away unless it acts like the Disk II controller, but interfaces to a different kind of drive. You'd probably need software. If you end up connecting the card and don't have a definite result, you can try measuring the lines on the IDC connector and compile data on the signals (an oscilloscope would be more useful, but multimeter measured analog signals might be sufficient in this case). In any case, if it's a floppy card for a standard PC drive (not an old one that comes with an enclosure), it probably won't provide power to the drive. That said, you'll need a powered drive to test that theory.
Best of luck with your interesting looking card.
P.S.
Betting those blue ceramic capacitors are on the voltage supply line.