Preheat the oven to 350 degrees F (175 degrees C).
Place apple slices in an 8 or 9 inch square baking dish. Spread the cranberry sauce over the apples. In a medium bowl, stir together the flour, oats, brown sugar, cinnamon, and butter until crumbly. Sprinkle over the apples and cranberry sauce, covering completely.
Bake for 45 minutes in the preheated oven, or until apples can be easily pierced with a knife and topping is browned.