For those who want to dive in to current applications,
there are two implementations of software digital cash that
I know of out there:

* The Magic Money (MM) system.  This is source code freeware, but 
for experimental purposes only, unless you arrange the appropriate 
licenses.  The client (used by vendors and customers) and server 
(token issuer) can be run over e-mail or sockets, and probably with
some modification over http.  MM implements a full online digital 
cash protocol, but it is written as an experimental system by 
and for programmers, so there is no good user interface, and 
there is no software connecting the server to financial networks 
or real banks.  This is the only digital cash software out
there where you can look at the source code, and hack it to your 
heart's content.

I don't have the latest ftp information (it keeps changing,
due to crazy U.S. crypto export restrictions access is
restricted to North Americans); query the newsgroup alt.security.pgp 
for the latest details.  At least two servers were set up
a few months ago for experiments; I don't know if they're
still running: contact Matt Thomlison (phantom@stein3.u.washington.edu) 
and Mike Duvos (mpd@netcom.com).  

* The commercial ECash software digital cash from David 
Chaum's company DigiCash. Chaum is the guru of digital cash, 
so I expect this will be a very solid implementation.  It 
runs over Mosaic, and from what I hear has a good user interface.  
It is somewhere near or in beta test.  http://digicash.support.nl 
for details, and pointers to Chaum's many fine papers,
which are necessary for understanding how the protocols
really work.

* The NetCash system.  This isn't digital cash, since
it has no privacy feature, but until ECash is released it
might make a good entry level system for some vendors
and customers.

There are probably over a dozen acedemicians working on new
or refined digital cash protocols, and several commercial smart
card based digital cash systems are likely under development
(including the Mondex trials currently underway in Britain).  
Hal Finney often posts good articles on new digital cash
protocols to the cypherpunks list (majordomo@toad.com), most
recently Stefan Brand's greatly improved offline protocol.
Cypherpunks also has excellent coverage of legal, political, 
and technical issues of cryptography in general, as do the 
newsgroups talk.politics.crypto, sci.crypt, and alt.security.pgp.
And it bears repeating, to fully learn the protocols
you'll need to dive in to the original papers in the _Crypto_
and _Eurocrypt_ conference proceedings.

Besides implementations, the most important work that I see
needs to be done right now is (1) the marketing studies, so 
that we can replace our speculations about desire
for privacy, customers and vendors outside the credit card
system, etc. with solid facts, (2) implementing the
interface of the digital cash server to current financial
networks (along with designing good legal and business
models: token server, bank, billing company, etc.), (3) modifying 
current online services to accept digital cash, with the 
verify/provide service sequence, and (4) designing full online 
business concepts and transaction protocols around digital cash, 
for example "information vending machines" run by part-time 
entrepreneurs.  I suspect that (3) and (4) are the best
fit to members of this list, and I'd be happy to consult
with folks seriously pursuing these tasks.

It's also good to keep in mind, as I pointed out in my
essay "Smart Contracts", that while the protocols are 
dubbed "digital cash", they really implement something 
more general, the digital bearer instrument, of which cash 
is only one example.  The protocol objects could just as
easily be tokens, coupons, bearer bonds, or a wide variety 
of other bearer instruments.  We might build in additional
features, such as activation dates, expiration dates, and
tear-off coupons for scheduled payments.  Perhaps we
could design new instruments that are especially useful 
for Internet information vending.

Nick Szabo                              szabo@netcom.com