Special equipment: a biscuit cutter or small melon baller and 2 pastry bags, optional
Slice the top and bottom from each apple and discard. Slice the apples into 1/2-inch circles. Use a biscuit cutter or small melon baller to cut a hole in the center of each to make a "donut."
Put the chocolate-hazelnut spread and peanut butter in separate pastry bags (or put in separate ziptop bags and snip off a corner).
Top the apple rings with either the chocolate-hazelnut spread, peanut butter or yogurt. (Pipe the chocolate-hazelnut spread or peanut butter, then spread carefully with a knife or offset spatula; spread the yogurt with a spoon.) Garnish each with a variety of the toppings.