LocalTalk is Apple's name for AppleTalk protocol running on an ad-hoc RS-422 serial-bus network. Speed is limited to some 200kbps, but the Newton actually does LocalTalk at 57600 bauds.
LocalTalk's inital use was to connect and network to expensive laser printers. It quickly found other uses, from file sharing onwards.
Old Mac hands will remember when AppleTalk meant both the protocol and the hardware it ran on. One early plug-compatible was Farralon's PhoneTalk hardware which used inexpensive telephone wiring to pass the signals around.
