This post concerns the past rather than the future, but I thought it was still relevant. I've posted previously about alternative currencies, and I've just come across a passage in Liza Picard's Restoration London describing the currency of the time:
There was a dire shortage of coins of small denominations, such as a housewife needed for everyday shopping. This had been an increasing problem since James I's day. It had reached such proportions that something was about to be done about it when the [English] Civil War broke out. Shopkeepers evolved a pragmatic solution: trade tokens. In the 1660s, there were 3,543 'tokeners' in the City, the suburbs and Westminster.
Tokens were usually made of lead, tin or copper, sometimes leather. They were mostly worth a halfpenny or a farthing; only the coffee-houses found it worth their while to issue 1d tokens. They were usually round, sometimes heart-shaped, square or hexagonal. They were about the size of a modern 1p or 5p piece. Shopkeepers kept boxes with compartments for each issuer. (They would need to cater only for those tokeners in the same shopping area - not all 3,543.) When they had enough, they returned them to the issuer, who changed them for silver or notes of hand.
In the short length of Chancery Lane, 28 shopkeepers issued tokens. In Seething Lane, where Elizabeth [Pepys] lived, we know that Ralph Bonnick at the Black Dog and Edward Radcliffe at the Pied Dog issued tokens for halfpennies, Thomas Rivers at the Grocer's Arms and William Vaston, chandler, issued tokens for a farthing; there may have been more whose tokens have not survived.
All this finished in the Great Fire of 1666, when everything went up in smoke. Still, it's interesting when you realise that modern or futuristic ideas have been practised hundreds of years ago.