[kazinator]

That's Ytalk; also ancient, and uses the same protocol.

https://linux.die.net/man/1/ytalk

I seem to recall seeing people use that around the undergraduate CS lab.

I should have mentioned that what was new (to me) when I was introduced to talk/ntalk was the concurrency of the split screen: both parties just clacking away at the same time

As a user of dial-up BBSes, I had often chatted 1:1 with sysops, nor as a sysop with users. The BBS sysop chat implementations were different/simpler; both parties were typing into the same space. This required manners: taking turns, letting the other people finish their sentence. That's the same like a Windows user being remotely assisted today: you and the remote admin can both move the mouse cursor or type into the same edit boxes.