As others have mentioned, it's the connector board for the external floppy.
@Johnnya101 @Nixontheknight The second floppy header actually connects to the external floppy cable (the cable that ultimately connects to the computer.) The female connector on the board is for daisy-chaining.
@jajan547 The little adapter board is still useful, though. It gives you real LED r/w status for any floppy drive. So if you stuff it somewhere between your floppy drive and your Mac's motherboard, you can route some LEDs to the front of your case and get real LED action. I did it on my IIci (fits perfectly under the drive cage.)