For the custard:
In a medium saucepan, combine 1/4 cup of the sugar, the gelatin, and the salt. Stir in the lemon juice, lime juice, limeade (or tequila), and orange juice (or Triple Sec). Stir well. In a medium glass dish, whip the egg yolks until they are light. Stir in the lime zest. Add to the saucepan and cook over low heat, stirring constantly, until the gelatin is dissolved, about 3 minutes. Remove from heat. Transfer to a plastic container and allow it to come to room temperature. Cover and refrigerate, stirring occasionally until the mixture has begun to gel, about 30 minutes.
For the meringue:
With an electric mixer, beat egg whites with cream of tartar until soft peaks form. Gradually beat in the sugar until stiff. Fold in beaten whipped cream.
Remove custard from refrigerator and fold in the meringue. Place the mixture, when finished folding, back into the refrigerator and let chill.
When serving rim your glass with sugar and pour chilled mousse into glass.