New old stock, boxed, Allied Telesyn AAUI to UTP (Unshielded Twisted Pair or 10baseT) transceiver for use with any Macintosh with an AAUI ethernet port. Does not require any driver software other than the ethernet software in Mac OS. Back in the day when ethernet came in three flavours; thick, thin and twisted pair, the transceiver was a way of building ethernet support into a Macintosh but allowing the type of ethernet to be decided by the transceiver you bought.