When Purdue's campus terminal network was finally wired directly to the CDC 6500 one could finally interact with a job running there. I wrote a chat program that would host conversations held on an append-only file. It was an experiment. We used it once.
I held the chat log in a persistent disk file. These were not commonly used and may have required my administrative privilege to create.
When the chat program launched from a terminal, I printed the chat log up to its end. I then prompted for input, wrote it to the (possibly advanced) end of file, and then printed any new text that might have arrived from other terminals.
We ran this one evening. Word got around. As the chat got longer it became hard to join the party because one had to read all prior conversation first.
Some people had 300 baud terminals that could print 30 characters per second. That put them at a distinct advantage over those with 110 baud connections printing at 10 characters per second.
User IDs were three characters long. Each text was so identified. Computing center staff had IDs that started with A. The operator's console ran as AAA. I was flattered to see AAA participate in our chat.