Using applesauce instead of butter...
I have been trying to bake low fat since my Dad had his heart attack in the early 90's.
I have found that most of the "substitute" ingredients produce baked goods that suck. Applesauce, pureed dates, bananas, yogurt, you name it. Gummy messes at worst, decent at best.
The good news is, sometimes you can just REDUCE the butter quite substantially, and still get a good product. Also, I find that skim milk is interchangeable with whole milk to no detriment in cakes. (cream is a different story)
The best butter-less recipes are the ones that just happen to be that way, not ones that you sub-ed. Many quick breads call for very little fat, and are pretty tasty.
But of course, hope springs eternal. If you find the magic bullet, POST!!!