An existing, growing system which uses a chain transaction model similar to Ripple's
Mike V
currencies for a while, and recently got a tip about a system which
the readers here may find relevant. The system uses transaction chains
for commodities as a means of moving goods between businesses, when
credit is sparse, and as a means of debt settlement.
This brochure on the website of the Anticrisis Settlement and
Commodity Centre, the organization behind the system (they now have
some 40 plus branches in Russia, and now expanding to London, Hong
Kong, and further), has a good overview of how it works:
http://docs.google.com/viewer?url=http://ascc.sterligoff.com/files/Info-Pack.pdf
There's also a short English interview with German Sterligov, the
Russian businessman, entrepreneur, and all around interesting
character who heads the ASCC, here:
http://www.youtube.com/watch?v=NGv5nSvMNek
If you happen to know Russian, I'd recommend some of the longer
interviews with him on YouTube and Google Video, where he goes into
more depth into the system and his objectives.
It currently has some downsides and limitations, such as being
proprietary, centrally managed, and geared for exchange among large
businesses, but as working, in demand implementation, it serves as a
proof-of-concept of the basic model of chain peer-to-peer
transactions, and as an example of a viable market point-of-entry for
comparable systems.