Zcash
The first real-world application to use Zero Knowledge Proofs. Pay with complete privacy and anonymity.
About
Zcash is a decentralized cryptocurrency focused on privacy and anonymity. It was the first project to implement zk-SNARKs, a novel form of zero-knowledge cryptography that gives its users the strongest privacy available in any digital currency. Describes itself as the 'https of blockchains' by protecting user freedom to save and spend as they like.
For more information, please refer to Zcash web page.