Electronic plans?

While electronic money has been an interesting problem for cryptography (see for example David Chaum's work), to-date use of digital cash has been relatively low-scale. One rare success has been Hong Kong's Octopus card system, which started as a transit payment system and has grown into a widely used electronic cash system. Another success is Canada's Interac network, which in 2000 at retail (in Canada) surpassed cash as a payment method.