Well, the chips on that board add up to it doing *something* interesting, but whatever it was it didn't interface directly with the NeXT's bus. (The wiring makes that obvious.) There's a handful of 4 bit binary counters, a few shift registers, and, most interesting, a couple of RS-422-compliant line drivers. If I had to take a wild guess it's some sort of serial data buffer or baud rate converter?