Not technically a mango (Mangifera indica), Mangifera casturi (or Kastoree) is a mango relative originally from Borneo, Indonesia that is a very small, round-oval fruit which turns purple is color.
We have two types of Casturi trees in the ground in West Palm Beach and did manage to fruit one in Loxahatchee Groves at one point.
The fruit are very small,round, with orange fibrous flesh, light in flavor which some compare to lychee. They have a purple, almost bluish appearance hanging from the tree
The flowers and fruit are completely resistant to anthracnose, but the flowers can get powdery mildew.