Combine rhubarb and sugar in a large kettle or dutch oven. Let stand 15 to 20 minutes or until sugar is moistened. Bring to boiling. Boil uncovered for 10 minutes stirring frequently. Add the raspberries and return to a boil. Boil hard for 5 to 6 minutes or until thick, stirring frequently. Remove from heat. Add gelatin; stir until dissolved. Ladle into half pint freezer jars leaving 1/2 inch head space. Let stand at room temp for several hours or until jam is set. Store in the refrigerator or freezer. Makes about 5 - half pints. Can be stored up to 3 weeks in the refrigerator or 1 year in the freezer!