To quote them:
"OnTap is a revolutionary new way to enjoy beer. Add our liquid flavor enhancer to a domestic light lager and enjoy a craft brew taste at a fraction of the cost. One bottle of OnTap holds enough to improve the flavor of a full 18-pack of standard 12oz. beers, depending on how much you use.
Just squeeze a few drops of one of OnTap's great flavors in to a glass of beer and you'll get a unique and great tasting beverage. Make each bottle or glass the same, or make each one different. Its up to you how each one tastes. The time has come to enjoy Your Beer, Your Way!" Personally I'm not sold on it. You CAN find good beer at low prices if you look around.