Preheat oven to 400 degrees F (175 degrees C).

In a large bowl, mix together rhubarb, blackberries, raspberries, blueberries and sliced apples. In a separate bowl, combine the sugar, cornstarch, cinnamon and nutmeg together and blend with the fruit.

Pour fruit mixture into a 9x13 inch glass baking dish.

For the topping: In a large bowl, mix the oatmeal, flour, brown sugar and 1/2 teaspoon cinnamon together. Add the butter in little pats and cut into the flour mixture until it looks crumbly, (no big chunks). Sprinkle over the fruit.

Bake at 400 degrees F (175 degrees C) for 30 to 35 minutes, or until topping is brown.