Cashu is a free and open-source Chaumian ecash system built for Bitcoin. It lets users hold and transfer ecash tokens offline, settling against the Lightning Network when needed. Nobody needs to know who you are, how much you hold, or with whom you transact.
Explanation of Chaumian eCash principles, blind signatures, and modern implementations like Cashu and Fedimint for private, custodial or federated ecash on Bitcoin.
Continuum of Bitcoin privacy from basic hygiene (address reuse avoidance, Tor) to advanced techniques (CoinJoin, Silent Payments, lightning, Nostr) — matched to user capability and threat model.