Arrange crackers in 6 (4 1/2 inch) tart pans or 1 (9-inch) tart pan with removable bottoms, breaking crackers to fit.
Sprinkle gelatin over lime juice in small saucepan; let stand to soften.
Stir over low heat until dissolved; cool.
Combine ricotta cheese and 14 cup yogurt in blender until smooth.
Pour into bowl.
Stir in remaining yogurt, 1/2 cup sugar, extract and 1 teaspoon grated lime peel.
Stir in cooled gelatin.
Pour over crackers; refrigerate.
Twist crown from pineapple.
Cut pineapple in half lengthwise.
Refrigerate one half for another use.
Cut fruit from shell of other half.
Cut fruit crosswise into thin slices.
Combine water, 1/4 cup sugar and cornstarch in saucepan.
Cook, stirring, until sauce boils and thickens.
Cool.
Add pineapple and 1 teaspoon shredded lime peel.
Arrange on top of tarts.