Roberts, Adam. Stone

Adam Roberts, Stone (2002). The protagonist of Stone, on a visit to the world Rain, discovers a currency of leaves. The unspoken joke is that on Rain, money does grow on trees! Trees and their leaves are also abundant: a local explains that because of this shrewd choice of currency, everyone on Rain is rich! But the Rain-dwellers do take their currency very seriously: when the protagonist finds themself curiously leaf-bereft, they really cannot buy anything. The episode has a satirical, proto-sf "traveler's tale" type feel to it. But at the same time, it feels possible to reconstruct a kind of economic system that makes almost perfect sense.

Rain is part of a broadly post-scarcity and utopian civilization. In this civilization, the puzzles of resource allocation are probably not the big ones we're used to nowadays -- posers like, "healthcare or nuclear deterrents?" -- but rather, masses and masses of infinitesimal puzzles. They are infinitesimal puzzles about the most efficient and fair way to enjoy peace and luxury together which, a bit like Stone's ubiquitous swarming nanotech, might accumulate into something fairly formidable. On a world where there's always enough to go around, should it go around clockwise or what? (You could call it "lowered stakes scarcity," or "estranged scarcity" or something).

Gathering leaves introduces a modicum of inconvenience, and you might plan your activities between bouts of leaf-gathering. Leaf currency, we may imagine, allows the Rain-dwellers to sustain a smidge of the quantifying and calculative rationality of homo economicus. Thrift is comprehensible to them. In the rainy climate, leaves probably turn to soggy sludge pretty quickly, so there's also a kind of Gesellian Freigeld aspect to their leaf currency -- a dampening of liquidity preference, if you will -- so nobody would bother hoarding leaves. And nobody bothers trying to lend leaves at interest, or allows themselves to be exploited to get some leaves. They just go get some leaves.  Nobody's opinions are given more weight just because they have a lot of leaves. Leaf-getting does not lend itself to Sisyphean graft nor entrepreneurial genius. If somebody has a lot of leaves, they're just somebody who has gone and got lots of leaves.

For other money trees, see Nalo Hopkinson, Clifford D. Simak, and Douglas Adams. Adams's proto-humans are strict quantity theorists with a match and a mission to control the money supply. That's what's clever about Rain, you see. It's always raining.