In a large saucepan, combine rhubarb and sugar; let stand for 1-1/2 hours, stirring occasionally.
Bring to a boil; cook, uncovered, for 10 minutes or until rhubarb is tender. Remove from the heat; stir in gelatin until dissolved. Stir in pie filling and extract if desired. Transfer to jars; cool. Cover and store in the refrigerator for up to 3 weeks. Yield: 5 cups.