Take 1/2 cup smooth peanut butter. Add one tsp. brown sugar, two tbs. soy sauce, two tbs. vinegar, and one tbs. Braggs (or fish sauce, or more soy sauce.) Mix. Thin to desired consistency with water. (My mother makes this, and I used to make it from memory. I would attempt to thin the sauce with vinegar and soy sauce. It was flavorful. Then I asked her about her secret ingredient: it's water.) Correct the seasoning- add whatever makes the whole thing taste the way you want. Also, possibly add grated ginger, grated garlic, or toasted sesame seeds.
It's good poured over noodles- in which case I advocate the old-school technique- or as a dipping sauce for summer rolls, satay, or crudites.