Preheat oven to 250 degrees F (120 degrees C). Line 2 baking sheets with parchment paper.

Cut about 1/4 inch off a corner of a heavy gallon-size resealable plastic bag, and push a large-size cake decorating tip (such as a star tip) into the opening. The fit should be tight.

In a small bowl, stir the gelatin mix with the sugar substitute. In a large bowl, using an electric mixer, beat the egg whites with cream of tartar and salt until stiff peaks form. As you beat the egg whites, gradually add the gelatin mixture, about 1 tablespoon at a time. Spoon the fluffy mixture into the prepared plastic bag, and gently squeeze and twist the bag to force the meringue mixture to the decorating tip. (Do not seal bag, so that air can escape.)

Squeeze the bag to place golf-ball size dollops of meringue mixture onto the prepared baking sheets. For a decorative effect, twist and lift as you place the cookie on the sheet, to make a pretty shape.

Bake in the preheated oven until the cookies are set and dry, about 1 hour and 30 minutes. Do not open oven door while baking. At end of baking time, turn off oven, open oven door, and allow the cookies to slowly cool in the oven before removing from baking sheets. Store in airtight container.