My girlfriend and I recently visited Costa Rica, and saw this fruit that we thought was a mangosteen, but was identified as a cainito. Unfortunately, we never got to try it!
I poked around on the web, and I think this is it:
Also known as caimito, star apple, golden leaf tree, abiaba, pomme du lait, estrella, milk fruit and aguay. Does anyone know where I might be able to obtain one?