Zcoin (XZC) is an open-source privacy-focused cryptocurrency token that launched in Sep 2016. Zcoin originally pioneered the use of Zerocoin to enable privacy but has since transitioned to a scheme called Sigma which is based on a paper by Jens Groth and Markulf Kohlweiss that reportedly allows greater scalability and removes the need for trusted setup in Zerocoin. With Zcoin’s Sigma feature, only the sender and receiver would be able to ascertain the exchange of funds in a given transaction, as no transaction histories are linked to the actual coins. Zcoin is also the creator of the Lelantus privacy protocol which improves Sigma's privacy and functionality.
https://zcoin.io/