ZCoin is the first full implementation of the Zerocoin Protocol, which allows users to have complete privacy via zero-knowledge proofs.

Many privacy crypto currencies are a mashup of code pulled from various other open source works backed by a strong marketing campaign (which requires a huge war chest of cash)

Zcoin (XZC) focuses on research and development. They were first to implement the Zerocoin protocol and isn’t a fork off some other project with small tweaks.