This post briefly describes some advocates of some strange ideas near the start of the twentieth century. I am avoiding socialists and Marxists in what Keynes called an "underworld" and an "army of heretics".
- Major C. H. Douglas: British engineer who inspired the Canadian social credit movement. I have not read enough to understand his A + B theorem, but I gather he explained depressions and recessions by an underconsumptionist theory.
- William Trufant Foster and Waddill Catchings: American writers and underconsumptionists. Hayek wrote some criticisms of them.
- Silvio Gesell: A german living in Argentina and later in the Soviet cabinet in Bavaria after World War I. Had a worldwide following. Advocated stamped money, in which money needed to be stamped each month to remain capable purchasing commodities. Money would no longer be as liquid. Savings would be more likely to be channeled into physical investments.
- J. A. Hodgson: Birtish journalist and prolific popular writer. Developed a theory of underconsumption, rejecting Say's law. His theory of imperialism influenced later Marxists.
- Henry George: American journalist and writer. His book Progress and Poverty started a worldwide movement, with followers today. Most well-known for the idea of a land value tax (LVT).
- Frederick Soddy: English chemist, 1921 Nobel laureate. Had ideas about how thermodynamics applied to economics. Advocated the abolishment of the gold standard. Claimed that debts must grow exponentially with compound interest, which cannot be supported by the real economy.
I am sure that some of these were associated with some political ideas I would reject. Wikipedia has Major Douglas and Frederick Soddy as anti-semites.