Grate zest from limes. Squeeze 2 teaspoons juice from one of the zested limes into a bowl. Process lime zest, sugar, and salt in a food processor until zest is coarsely ground.
Core apple, then cut in half and slice thinly. Add to lime juice, and toss. Peel mango; cut flesh away from pit, and slice thinly. Halve papaya, remove seeds, and slice thinly.
Arrange apple, mango, and papaya on a serving platter or plates. Sprinkle with some of the sugared lime zest, and serve remaining zest mixture on the side.