Island of Kesmai
One of the first commercial multiplayer role-playing games, played over CompuServe by the hour.
Kelton Flinn and John Taylor started writing the game at the University of Virginia around 1980 and launched it on CompuServe in 1985. The world was drawn in ASCII characters in a window beside the text, much like a roguelike, and players fought monsters and each other on a shared island. Death had teeth, and gear could be lost.
What made it famous was the business model: CompuServe billed by the connected hour, and an evening on the island could cost more than a boxed game at the shop. Kesmai built on the same idea with the flight sim Air Warrior and was bought by Electronic Arts in 1999. The subscription economics that later carried MMOs were first tested here — with a meter running.