They're definitely not illegal, although certain forms are illegal. That law only covers attempts to create currencies that could be mistaken for US dollars. Ot

They're definitely not illegal, although certain forms are illegal. That law only covers attempts to create currencies that could be mistaken for US dollars. Other systems are illegal because they amount to an unregulated form of banking, or because they are used for laundering. For tax: it depends on the currency in question. Barter systems that use a currency to settle barter accounts are taxed as normal income. Systems such as Time Dollars are considered tax free because they are used for non-commercial activities (http://www.timebanks.org/faqs.htm#taxexempt http://www.timebanks.org/faqs.htm#taxexempt). In China, there exists at least one system that is considered tax-exempt, except when the currency is exchanged for real currency, in which case it is subject to tax.