Cashu is a privacy-focused electronic cash system built on top of Bitcoin. It is based on the cryptographic protocol developed by David Chaum in the 1980s, which is designed to allow for anonymous and secure transactions.

The system is intended to provide privacy and anonymity for users of custodial Bitcoin applications, such as exchanges or wallets.

Cashu is open source, which means that anyone can inspect the code and contribute to its development. This transparency helps to ensure the security and reliability of the system.