PureVia All Natural Sweetener is first not really quite zero calorie, as has been pointed out elsewhere it contains 2 grams of Carbohydrates which convert to some small percentage of calories but less than 1/2 of 1 calorie.  Splenda by contrast is able label itself 0% of carbs as it has less than 1 gram.  Honestly all of this is pretty much in the range of meaningless.

PureVia is made primarily from Erithritol, Isomaltulose and the third listed ingredient Reb A which is an extract from the Stevia Plant and is where most of the sweetness comes from although it is only the third and final ingredient...