Wikipedia
Zerocoin
Zerocoin is a cryptocurrency proposed by Johns Hopkins University professor Matthew D. Green and graduate students Ian Miers and Christina Garman as an extension to the bitcoin protocol that would add true cryptographic anonymity to bitcoin transactions. Zerocoin was first implemented into a fully functional cryptocurrency by Gary Le and Poramin Insom, as the Moneta cryptocurrency. Zerocoin provides anonymity by the introduction of a separate mixing service known as zerocoin that is stored in the bitcoin blockchain. Though originally proposed for use with the bitcoin network, zerocoin could be integrated into any cryptocurrency.