there is no money involved. only trading of goods and services. i think some of these groups have their own currency system. eg if i carry out a service for someone then instead of giving a service or some goods back to me they give me x amount of credits which i can then spend on service or goods from someone else. some creases will need to be ironed out to make it shariah compliant, but if people are really interested in moving away from interest based currencies and giving less tax to the governement as much as possible then it can work.