The GNU Taler project:
We are building an anonymous, taxable payment system using modern cryptography. Customers will use traditional money transfers to send money to a digital Exchange and in return receive (anonymized) digital cash. Customers can use this digital cash to anonymously pay Merchants. Merchants can redeem the digital cash for traditional money at the digital Exchange. As Merchants are not anonymous, they can be taxed, enabling income or sales taxes to be withheld by the state while providing anonymity for Customers.