I was hacking on PLATO, making these rather dopey "now, johnny" computer-assisted instruction lessons for basic math and some biomedicine. The college existed to help teach basic job skills to people who had passed through the Chicago public schools without learning anything. Medical technician was one big target job market. I think my crowning achievement was to make an animation of the human heart cycle, including sound effects from the compressed air actuators that were a feature of each PLATO terminal.
I was a PLATO user in high school and actually my first real job was on PLATO (at Malcolm X College
One notable PLATO feature was that they had an extended charset which included a variety of superscript codes and drawing mode codes, which means you could code up elaborate animations in text, so people would craft themselves custom signatures like a bow firing an arrow and the like.
PLATO also had communication tools that were quite far in advance of ARPA-world stuff (which I switched to when I went to MIT in 1976). Things like realtime group chat and multiplayer games. I don't think there was direct technical influence from PLATO to ARPA/PARC, but I would guess there was cross-pollination of ideas. PLATO also ran on CDC hardware, which was a slightly different world from the DEC-heavy universe of ARPA.