PLATO Notes is 50 years old as of today. One of the world's first online message forum applications, it was an instant hit on the PLATO system at the University of Illinois, and rapidly hastened the online culture that grew in the years 1973-74 to include message forums, instant messaging, screen sharing, multi-user chat rooms, multiplayer games, online support chat, and many other features that we've all come to take for granted in the 2000s.

Article from 2013:

https://medium.com/@brianstorms/plato-notes-released-40-years-ago-today-13392e324814