The cowry was used as an international currency for thousands of years and wasn't backed by any government. All it was was seashells that were a limited supply resource. In major usage, it was used all the way from Africa to Hawaii. I think most people look at currencies with an incredibly narrow view of history.

^ Worth noting, that this is relatively modern history. It's usage stopped as a currency in the mid 20th century. At the beginning of the 20th century, some african countries still accepted it as taxes