Substituting apple sauce will dramatically reduce the fat and caloric levels, reduce the need for sugar and add flavor and natural sweetness to baked goods. Experimentation works best for determining what levels of substitution are acceptable to you and your family's palate. The best products may not be in your cupboard today, but don't rule them out until you try them. Apple sauce is an especially good fat substitute in gingerbread, chocolate cakes, white cakes and recipes in which you don't want to change the original flavor.
Apple butter is terrific in spice cakes and bran muffins.
Try apple juice in carrot cakes and coffee cakes. Start by looking at your recipe to determine if it already contains a fat substitute. If it does, that is your best choice, and you only need to increase the amount of the product as you eliminate the fat. If it doesn't, consider the flavors that would best blend with that recipe. Baked goods recipes are better candidates for fat reduction or elimination.