Plato often gets overlooked, but it was highly influential. A well written book on it is: "The Friendly Orange Glow: The Untold Story of the PLATO System and the Dawn of Cyberculture"

Quoting myself from 2023, in a discussion of computer history books:<https://news.ycombinator.com/item?id=35405385>

The Friendly Orange Glow, about PLATO. Not because PLATO was super-influential on the later industry—far from it, with only minor exceptions—but that doesn't mean that it doesn't deserve examination.