Place 2 cups of water and the sugar in a medium nonreactive saucepan, along with cinnamon stick and vanilla bean if using. Bring to a boil.
Add the rhubarb and prunes, and ground cinnamon and vanilla extract if using, and simmer over low heat until rhubarb is just tender 7-10 minutes. Don’t allow it to get too soft.
Using a slotted spoon, remove the rhubarb and prunes and transfer to a large serving bowl. Separate the oranges into segments, then slice each into thirds horizontally, and add them to the bowl, along with the raspberries.
Boil the syrup remaining in the saucepan over medium-high heat until reduced by about half. Remove the cinnamon stick and vanilla bean, if using, and pour the hot syrup over the fruit. Stir well.
Let fruit cool to room temperature, then cover and refrigerate for several hours or up to four days.