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Groupcash: A Commodity-Backed Cryptographic Complementary Currencies System

The goal of groupcash is to make it easier, cheaper and safer for anybody to run their own complementary currency.

For that it defines a set of specifications on which compatible software systems can be built which can be used for managing and trading in different kinds of independently run currencies.

The following figure illustrates this structure which is also the structure of this document.



Complementary currencies are a great tool to solve many different kind of problems, so they come in different forms and shapes. Which problems there are and how they are solved with groupcash, you can read in the manifesto.

How different kind of currencies solving different problems can be run with groupcash is described in the use-cases document.

If a complementary currency can be successfully implemented and run in depends on the community but also on the software systems and specifications. An attempt to list the underlying assumptions with the goal of collecting knowledge about pitfalls and challenges can be found here.

The commonality of all groupcash currencies is that they're commodity-backed, meaning that they are based on delivery promises of goods or services. Forgery and fraud is prevented by cryptographic algorithms (i.e. math + computers) instead of coins, bills and banks - decreasing the cost of starting and running a secure currency.


Software Systems

While complementary could be and were run manually for many thousand years, software can make the task a lot easier and cheaper. And because of its cryptographic property, groupcash currencies require computers and software.

The same property allows for a wide range of different architectures. Because no central database is needed, currencies can be run in a peer-to-peer network or in a server/client architecture, with either native clients or as a web application.

Software systems implementing the groupcash specification can be found on the web (as soon as they exist) and are also collected in the groupcash organization on github


The core of groupcash is a set of specifications that facilitate interoperability between software systems with which currencies can be run. These specify a design, based on digital signatures, the algorithms to create and verify these signatures, protocols for trading between systems and formats how currency units and other objects can be represented virtually and physically.

Related projects

While its approach and implementations are (hopefully) unique, groupcash is not the only project trying to make complementary currencies more approachable. If you know would like to add to this list or are interested in collaborating, please contact us.

  • MetaCurrency Project - "The MetaCurrency Project is building the tools and technology platforms to open source the next economy."
  • OpenMoney - "Open money is a means of exchange freely available to all. Any community, any association - indeed, any body - can have their own money."
  • New Currency Frontiers "We invite you to explore innovative interpretations of money, economics and society which are resulting in a new way of thinking about our future."
  • CommunityForge - "Community Forge is a non-profit organization that designs, develops and distributes tools around complementary currencies."



The groupcash system is released under the MIT License