Haven't had the Wendy's sauce you mentioned, but here are two:
Chinese Duck Sauce - we really like this one
3 cups plums, peeled and chopped
2 cups apples, peeled and chopped
1 cup water
1/4 cup cider vinegar
1/4 cup light brown sugar, packed
1/4 teaspoon salt
2-3 medium garlic cloves, minced
1/2 teaspoon dry mustard
Combine all ingredients in a med-sized pan, and bring to a boil.
Reduce heat, and simmer uncovered until the fruit is very soft, about 30 mins., or longer.
Cool to room temperature. Mix well using blender or food processor
Store in the refrigerator.
Spicy Duck Sauce - came across this one some time back but haven't tried it yet
1/2 tsp. ground cinnamon
1/2 tsp. ground ginger
1/8 tsp. ground allspice
2 tbsp. dry sherry
2 tbsp. honey
1 tbsp. chili sauce
1 tbsp. soy sauce
1 clove garlic, minced
Combine all ingredients. Mix well.