Combine apples, apricots, prunes, and water in a large saucepan; let stand 1 hour.
Stir in sugar, and add cinnamon. Cover, and simmer over medium heat 40 minutes or until fruit is tender. Transfer fruit to a 1-quart serving dish, leaving liquid in saucepan; discard cinnamon.
Add cornstarch to liquid in saucepan, mixing well. Cook over medium heat, stirring occasionally, 15 minutes or until mixture begins to thicken. Add lemon slices, and pour over fruit in bowl. Cover and chill thoroughly. Serve in chilled bowls as a dessert soup.
Note: Dried Fruit Soup may be served warm, if desired.