Mangosteen contains xanthones, antioxidants that could have health benefits. As usual, more research is needed. (Antioxidants have proven financial benefits, though, for the functional food industry.) The astringent rind houses the antioxidants, while the flesh only provides flavor.
It has been used for traditional Chinese medicine for centuries. However, the U.S. would not import it until 2007, when fruit irradiation was allowed.
Here are some other gums: