Place egg whites in a mixing bowl; allow to stand at room temperature for 30 minutes. Line a large cookie sheet with parchment paper or foil; set aside.
Preheat oven to 300 degrees F. Add vinegar and salt to egg whites. Beat with an electric mixer on high speed until soft peaks form (tips curl). Gradually add sugar and the dry gelatin, beating until stiff peaks form (tips stand straight). Spoon mixture into a pastry bag fitted with a large star tip (at least 1/2-inch opening). Pipe stars, about 1 inch wide and 1 inch tall, onto prepared cookie sheet.
Bake for 18 to 20 minutes or until dry but not brown. Turn off oven and let meringues dry in oven for another 15 minutes. Peel meringues from paper and let cool on wire racks. If desired, decorate by dipping tops or bottoms in melted chocolate, drizzling chocolate over tops, or sprinkling with powdered sugar. Place on waxed paper until chocolate is set.