From the Wikipedia at http://en.wikipedia.org/wiki/Alternative_currency
"Alternative currency is a term that refers to any currency used as an alternative to the dominant national or multinational currency systems (usually referred to as national or fiat money). Alternative currencies can be carefully created by an individual, corporation, or organization, they can be created by national, state, or local governments, or they can arise naturally as people begin to use a certain commodity as a currency. Mutual credit is a form of alternative currency, and thus any form of lending that does not go through the banking system can be considered form of alternative currency.
When used in combination with or when designed to work in combination with national or multinational fiat currencies they can be referred to as Complementary Currencies. If the use of an alternative currency is limited to a certain region, they are called Local Currencies." (http://en.wikipedia.org/wiki/Alternative_currency)
Such currencies are either time-based (each hour of work is considered equal), or have a value that can be negotiated (LETS
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