Except that my mom made me Rhubarb Sauce pretty frequently when I was growing up. It was my second-favorite way to eat rhubarb, and it does NOT have any apples. I think its full official name was Rhubarb-Strawberry Sauce, and it's chopped rhubarb, strawberries, sugar, and water, cooked down until it all flows together.
Rhubarb is a very sour and astringent fruit*, and it's hard to cook with. I do love the flavor when things go well, though. I think it will make an excellent counterbalance to the naturally sweet and mild nature of applesauce.
It totally rocked in the peach crumble we gave out a couple years ago as Christmas gifts. Peach Crumble, like any other fruit crumble, is basically (select a fruit) in a heavy syrup (better when thickened with a bit of cornstarch), with a crumbled brown sugar, butter, and oatmeal layer on top, baked in the oven. Apple is the most commonly used fruit, but peaches are great too, except they tend to be a bit too thick and sweet. If you don't get enough crumbly topping in each bite, it's pretty cloying.
So in a flash of inspiration, I made a crumble that was about 85% peaches, 10% rhubarb, and 5% raisins. The raisins did two things: made the flavor more complex and interesting, and made the appearance more interesting. The topping is beige, the peaches are a faded orange (which is to say, light brown), so it's all fairly bland. The black dots of the raisins, and the occasional pop of green or red from the rhubarb, really add to the appearance. The sour bite of the rhubarb, as expected, cut right through the sticky-sweet of the peach.
I look forward to figuring out the tastiest ratio of rhubarb to applesauce, as well. Especially since I'll have to eat the 'failures.' Mmmmm.
*"But but but! Rhubarb isn't a fruit!"? Of course it is. Do not make the common mistake of confusing the botanical meaning (Merriam-Webster, 'fruit' 1b(1) "the usu. edible reproductive body of a seed plant; esp : one having a sweet pulp associated with the seed") with the culinary one (Merriam-Webster, 'fruit' 1b(2) "a succulent plant part (as the petioles of a rhubarb plant) used chiefly in a dessert or sweet course")