It was not demonstrated at a global scale but the merchant thinker Silvio Gesell, whom Keyes and Irving Fisher both praised, describes it in his book, The Natrual Economic Order. That is the book that inspired a couple demonstrations of the concept, one in Germany, one in Austria, both so wildly successful central authority shut them down. The fee was to stop the unjust accumunlation of money now used to manipulate markets. Its different from inflation becasue it is a monthy 1% fee to restore its full value. Can't do that with inflation. You can get the book online for free. chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.naturalmoney.org/NaturalEconomicOrder.pdf