My last setting had regional apocalypse due to the collapse of their Roman Empire equivalent, which resulted in no national currency since the new feudal regime was so incoherent. There were, however, several local currencies that were gaining traction, such as:

• The goblins had a long-standing traditional currency system of specie coins, similar to that in the dnd handbook. However, anyone who wanted to mint currency could. This resulted in what could best be described as a deciduous economy. In the winter, goblin smiths would try to cheat the system by forging random gold, silver, and copper trinkets into coins to buy food with, resulting in rampant inflation. By the time spring rolls around and food starts becoming plentiful again, frustrated goblin smiths begin melting down their near-worthless coins into much more valuable jewelry and trinkets to sell, resulting in a period of rapid deflation until prices stabilize again in the fall. Often the values of the specie coins would inflate and deflate at different rates, resulting in periods where copper coins were more valuable than gold and silver coins but less valuable than bronze coins. Unsurprisingly, non-goblins tended not to bother with goblin currency.
• Most parts of the local Marches ran on a system of favors. I would have kept track of my player's reputations as a sort of credit score, but i decided to ignore this after one player lost his mind at the idea of not being able to buy things with those dolla dolla bills he provably did not have.
• A currency system gaining popularity was formed in a local city, which resembled the British LSD system but where one pound was 360 pence, and the values of the other coins corresponded to the prime factors of 360. Very logical, and I am sure my problem player would have lost his damn mind at having to do actual math to buy things.
• The nobility did not need to bother with currency, and never have. They simply conducted barter in bulk, backed by favors and local prestige. Exchange rates were very stable. As a result, they tended to use whole 5-pound ingots of precious metals as a form of currency when barter would be unnecessarily time-consuming. However, they seemed to see barter as the more civilized form of trade, since you had to actually conduct diplomacy with your fellow nobility to make it happen, so currencies have had to overcome the stigma of being the uncivilized tool of goblins and peasants to become popular. This was, in fact, the main factor behind why a dominant currency had not emerged in the last century.

“Credits”, which is gold IN SPAAAACE. The thing is, if you’re running a merchant campaign, currencies, jurisdictions, red tape, bribery, and smuggling can be fun. Otherwise maybe don’t even bother with money, the quest to findwhat you’re looking for is much more fun.

I'm afraid I don't remember the name of the system or else I'd link the rules, but I do remember playing a game where I really liked what they did with inventory and currency.

Basically, the game divorced the rules from the settings' currency entirely. So if you're into homebrew, that means it works equally well with gold, credit chips, reputation, bottle caps, and seashells

When you defeated a monster, finished a quest, or found hidden treasure, you would acquire LOOT. Get ten LOOT and you level up at the end of the adventure.

Instead of writing down and purchasing all of your basic equipment, you would have a certain number of GEAR points. If you found you were in a situation where you needed some item, you could mark off one of your GEAR to retroactively have brought that item with you.

I liked it because it sped up play and was super newbie friendly. You no longer run into a situation where a career adventurer plum forgot to buy torches before spelunking. It also meant you didn't have to roll a check for each item in the dragon's hoard to see if you could afford to feed your hirelings.

If that system sounds familiar to anyone, please let me know. I wouldn't mind taking it for a spin again

https://troypress.com/wealth-systems-in-rpgs/

Letters of Credit can lead to side quest.

Eclipse phase has a pretty cool reputation economy. You don't use money but network and reputation to get things (mostly info and access to fablab, it's a post abundance economic)

@Shkshkshk @rpg
Poland calls their coins 'gold' and 'silver' (though silver are now worthless due to inflation), so the USD doesn't necessarily have any relation.

I went with 1gp = 10sp = 1000 cp, so people could carry coinage more easily.

I can think of a couple systems that don't use gold (or any other straight currency) :

The One Ring uses treasures as a measure of wealth, which above set amounts grows and gives you access to more. It's not about spending your treasures, you're not buying goods for currency (most of the time), instead you can afford stuff depending on your level of wealth.

Warhammer Rogue Trader (40k) while not a ttrpg still offers an interesting alternative. Since you're extremely wealthy, earning and spending currency wouldn't make much sense on a small scale, so instead you gain reputation with various factions by trading with them, which in turn gives you access to items you can grab freely.

The idea is the same, rather than using currency you have a measure of what you have access to. It can evolve up or down, varying what you can get over time, without the hassle of book keeping (or verty little of it).

The best currency is obviously tally sticks.

I joke - I haven't used this in a game. It is interesting, though. From what I understand of history, the vast majority of people used a gift economy, barter, and what was essentially a credit system to get what they needed. The idea of the adventurers 'buying' their equipment on credit by owing the blacksmith a portion of loot later does raise some ideas.

Also tally sticks are where we get the phrase 'stock holder'; the one who loaned the goods kept the larger end of the split tally, which was called the stock.

The opportunity for shenanigans is rife with something akin to Rai Stones