Zcash is a Proof-of-Work (PoW) cryptocurrency designed to address some of the inherent flaws of Bitcoin e.g., lack of fungibility. Zcash has relied on a set of zero-knowledge proofs called zk-SNARKs to improve anonymity and thus fungibility.
In the Zcash network, addresses are either private ("z-addresses") or transparent/public ("t-addresses"). These two address types are interoperable.
According to the team, some of its key features include low-fee transactions, encrypted memos (allows the sender to include relevant information to the receiver), payment disclosure (allows disclose transaction-specific details to third parties), multi-sig transactions, and transaction expiration (transaction expire after a specific number of blocks if not mined).
Initially built on the Zerocash protocol, it has relied on Sapling since late 2018, part of its continuous improvement strategy. Sapling has led to efficiency improvements for shielded transactions (lower memory requirements), decoupled spend authority (i.e., hardware for zero-knowledge proof is independent from hardware to sign transactions), and an improved key system (allowing shielded addresses the ability to view incoming and outgoing transaction details without revealing private keys).