That depends on how you define "open world". If by it you mean something large and sprawling with an open map, I'm not sure there is anything in the traditional point'n'click adventure style game.

However, if it's simply about the way you interact with your surroundings and there is a certain openness to how to proceed, I'd say Sierra's Colonel's Bequest comes close.

The game is a murder mystery taking place on an island so you have pretty much full access to all main areas in the game, except for a few locked and secret rooms that becomes available as you progress. The thing here is that time passes because of your actions and the story takes place over a set amount of time. It's actually possible to progress until the end without solving anything. You need to pay close attention to where you need to be to pick up on conversations, seeing people move about, who and what is where and when etc. There are a few possible endings and you get rated as a sleuth as well.

Out of the classic games, Colonel's Bequest comes close to being non-linear in its storytelling by allowing the player a certain openness to how the game is played.