I once had a very old recipe for root beer using actual roots and herbs. Seem like there was licorice, sassafras, molasses, and what all, that I scrounged in health food stores. For carbonation you added a bit of yeast and capped the bottles. There was a brief period when the sugars and yeast allowed just the right carbonation to taste a few bottles, before they all over pressurized and blew up. It was a fun experiment and the flavor was unique.
I've seen some connoisseur type root beer brands around.