Patsy,
Great idea to make rhubarb sauce instead of applesauce, perfect for this time of year when apples are poor quality or flown in from the southern hemisphere.

To make it I would first cook rhubarb with the least amount of water that will keep it from sticking and when it's fork tender, add 1/3 of the sugar ratio called for in a recipe for rhubarb pie or crisp, and cook until sugar is dissolved, being wary of scorching. This approach means I could thin it with water (or apple juice or cranberry juice) if too thick, sweeten it more if too sour, until I know what amounts work for my taste.

To serve, I would substitute directly for warm or cold applesauce--alongside pork, chicken, venisor or lamb. It could also subsitute for red currant jelly served with meats. Usually I don't fancy the taste of fruit with beef or goat although there may be certain exceptions, not that I can think of them right now.

Rhubarb sauce might work well atop porridge, or sweeten it a bit more and put it hot over ice cream, maybe topped with a drizzle of caramel sauce too.