In one important respect, what we call "New Keynesian" macroeconomic models are in fact New Gesellian macroeconomic models. That's only in one respect, but it is important.
Silvio Gesell proposed a tax on currency. The higher the tax rate, the faster people would spend that currency. A tax is a negative subsidy. The higher the subsidy rate, the slower people would spend that currency.
Another name for a subsidy on currency is paying interest on currency. If that interest rate is 5%, for every $100 currency you hold, the bank that issued that currency pays you $5 currency per year.