DigiCash (1989, David Chaum) Cryptographic digital cash, blind signatures, anonymous payments.

eCash (early 1990s, David Chaum) Product of DigiCash, first untraceable online payment system.

e-gold (1996) Digital currency backed by gold, centralized, shut down by U.S. government.

b-money (1998, Wei Dai) Early proposal for decentralized money, introduced network consensus ideas.

Bit Gold (1998–2005, Nick Szabo) Proof-of-work digital currency prototype, major Bitcoin influence.

Hashcash (1997, Adam Back) Proof-of-work system to prevent email spam, tech reused in Bitcoin mining.

CyberCash (1994) Secure online credit card payments, more a payment gateway than cash.

Mondex (early 1990s) Smart card-based cash system, bought by Mastercard.

Liberty Reserve (2006) Centralized anonymous money transfer, shut down for money laundering.

Flooz (late 1990s) Internet currency used for online shopping, collapsed after dot-com bust.

Beenz (late 1990s) Loyalty point system marketed as “Internet money,” also failed after dot-com bust.

RPOW (Reusable Proof of Work) (2004, Hal Finney) System for reusing proof-of-work tokens, early Bitcoin-related experiment.