Botanically, "pomme de cajou," or cashew apple, is not a fruit at all; it's merely the swollen stalk of Anacardium occidentale, whose true fruit is what's better known as the cashew nut. Click on this photo of Zena pomme de cajou confiture (450 g.; $4.99), from Senegal, and you can take a closer look at how the knobby nuts perch on the end of the red or yellow cashew apples (whether the colors indicate different cultivars or varying degrees of ripeness, I don't know.) And the taste? Zena's confiture has some of the lusciousness of figs, but with a brighter flavor and a trace of tartness.
Darou Salam doesn't have a very large selection, but this friendly West African market does stock several other Zena varieties, including mango and papaya.
Darou Salam Market
235 West 116th St. (Frederick Douglass-Adam Clayton Powell Jr. Blvds.)