In a large bowl, combine rhubarb and sugar; allow to stand over night. Transfer to a large saucepan and bring to a boil. Reduce heat and simmer for 10 minutes. Meanwhile, dice peaches and add with filling to saucepan; return to boiling. Remove from heat; add gelatin and stir until dissolved. Spoon into canning jars or freezer containers. Cool completely. Refrigerate or freeze. Yield: About 7 half-pints