That Talkomatic screen shot was done in the last year or so (I'm one of the participants) on the Cyber1 system. It's the original program from the '70s, though, running on an emulated CDC 6500 (or thereabouts) that's running PLATO.
The Unix "talk" program is a two-person version of it. PLATO also had (has) something called TERM-talk, where both terminals are put into a mode where each sees the other's output, then just lets each type on their own line. You'd see the other person typing on their line, character by character, as you type on your own line. You could also switch to where one person could continue on doing other things while the other watched (and commented).
We also had forums and e-mail in 1974 (known as notesfiles and personal notes; Lotus Notes was created by one of the creators of the notesfile system, Ray Ozzie), and networked access between different PLATO systems across the country (and world) a few years later (pre-Internet).