There was also `write` [0]. It would literally parse /etc/utmp [1] to find out which terminal the recepient user was logged on, then it would open that terminal and write(2) the message to it. Ah, wonderful user isolation.
I still use posix write [1] if there is an incident and i want to talk to the other admins that all try to fix sth. Quite fünf AS the younger ones are always Quote puzzled and feel caught...
[1] https://manpages.org/write