Privacy is a core characteristic of cryptocurrencies. Despite mainstream conception, however, it is not the primary goal of cryptocurrencies like Bitcoin (BTC) or Ether (ETH), and is more of an ancillary benefit of using cryptography. The situation is altogether different for cryptocurrencies that seek to maximize anonymity when transacting on the network.
Networks like Monero (XMR) and ZCash (ZEC) have soared in popularity, making up part of the handful of leading cryptocurrencies by market cap based on strong guarantees of privacy. Both blockchains offer users virtually complete privacy assurances — Monero with the CryptoNote technology suite, and ZCash deploying the powerful cryptographic primitive zk-SNARKs, offer users virtually complete privacy assurances.