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.

[0] https://man.cat-v.org/unix-6th/1/write

[1] https://man.cat-v.org/unix-6th/5/utmp