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.
http://www.snarkout.org/archives/2003/12/08/
http://www.globalideasbank.org/BOV/BV-102.HTML
http://www.reinventingmoney.com/worglCurrDemurr.php
http://www.futureofmoneysummit.com/pr-terra.php
http://wiki.uniteddiversity.com/money_links
http://www.findarticles.com/cf_dls/m0254/4_57/53449308/p1/article.jhtml
There is an entry about tokens issued in the 1660s towards the end of this page:
http://www.pepysdiary.com/p/316.php
The information is largely taken from "Taverns and Tokens of Pepys' London" published in 1976 and written by George Berry. There's a copy in London's Guildhall Library which is open for anyone to use.
Like many other unorthodox forms of money, they were technically illegal - being outside governmental control - and were meant to be used for one specific purpose (in this case, spent in one location only) but their use tended to spread.
I know that two years ago (and maybe there still is) there were a group of people in Walthamstow, north-east London who devised their own non-monetary, non-physical currency (I forget what it was called). The users were mostly on the liberal or the left of the political spectrum.
It was supposed to help people who had little spare cash but skills that they could barter (sorry I keep speaking in the past tense; it may still be in existence). For example, an old lady could babysit some children and receive 20 notional "Walthamstow Pounds" = WPs (or whatever they are called) and use that and any other WPs that she already had to buy something else from a third party, i.e. it is a cashless community.
The advantages included that you didn't have to trade in a one-to-one basis; you could get WPs from one person and spend them with another.
The disadvantages included that, because of the nature of the people while there were a lot of people able to teach French, play the piano and fix computers; there were very few who could do plumbing or fix the electrics. And prices were skewed accordingly.