I almost forgot, but I actually started out reading digital books on this Sony Bookman in the early 1990s. Not sure if that was the actual name, but it was a cool clamshell device for its time. Unfortunately Sony never really supported it. It was difficult to find books for it, and they were in mini CD disc format. A great idea which Sony let die due to lack of available books.

I think the model I owned looked different from this one, but that was 25+ years ago.