PHONE (VMS)
The VMS answer to talk: a split-screen real-time chat with telephone vocabulary all the way down to the receiver.
The command shipped with DEC's VMS and worked both between users on the same machine and across DECnet, where you addressed someone as NODE::USER. The person being called got a beep and a message that someone was "phoning", and picked up with PHONE ANSWER. The screen then split into panes showing both parties' keystrokes letter by letter, typos and backspaces included. Commands like DIAL, HANGUP, REJECT and HOLD were issued after a percent sign, and more than two people could join the same call.
At universities with VAX clusters, PHONE was the social network before anyone called it that — and SET BROADCAST was there for anyone who wanted to get some work done, much like mesg on Unix.