WUZ is a simple and short humorous fantasy game that contains adult content - depending on your input. This was a ground-breaking game in 1989. You have the option to choose to play as male or female. Then you have the option to choose between being straight or gay. Your choices determine the responses of the game. (The paths are basically the same and very simple.)
While certainly not the first IF game to offer gender choice, this may have been the first to offer choice of orientation. This is a very short game with very easy puzzles. It is your choice what you wish to do to the characters you meet. In 1989 this was pushing the boundaries - today it'd be R-rated, if that.