Monetary Worldbuilding
Gold pieces, credits, Argentine pesos, whatever you call it, money is always a reward in itself and a stable, easy concept to grasp across most media. Because of this, when we make even little changes to how it functions, we can deliver an authentic and fresh vision to our worlds.
What IS your money?
In the videogame Caves of Qud (inspired by Gamma World, which was in turn inspired by Metamorphosis Alpha, one of the first science fiction TTRPGs), money is water because, in that post-apocalyptic world, water is a crucial need for almost every species to survive.
When you are designing a currency, I recommend choosing something useful and common, but not too easy to access, whether because of its scarcity and necessity for survival (oxygen, water, food) or because it is gatekept by power structures that dictate its production (contemporary currencies like the dollar, salt, cryptocurrencies, or gold pieces). Sometimes, it’s a combination of both.
What this does is establish the powerful groups or ecosystems toward which the majority of people will gravitate. Silver pieces will flow from rich merchants and nobles, while cryptocurrency will be gatekept by worldwide banks dominated by a combination of the most important nations and corporations.
What can your money BUY?
This is where the interesting part comes in.
Following the example from Caves of Qud, water is not only a survival tool, but also a cultural and political one. You can "share a drink" with the leader of a faction, increasing your reputation with that group while gaining enmity from their rivals.
This is the part where you think about WHAT you actually gain from spending or trading this resource. Maybe money in a certain region is only used to make big purchases like baronies, houses, ships, or farms, while in others, you can use it to buy people's loyalty, positions of privilege, and the like.
Perhaps you have different types of currency that mean different things to different people, which brings us to the final point.
What TYPES of money are there?
Now you repeat this process for a few different types of currencies.
The easiest example is in classic fantasy: gold is reserved for buying art and constructions like castles and fortresses, silver is for high-craftsmanship objects like armor, swords, and spyglasses, and finally, copper is for mundane things like food, simple clothes, and tools.
But you can go a step further. Maybe a guild of wizards only trades their spells for magic ink or stardust. A certain cryptocurrency might only be usable to buy and trade different AIs designed for specific tasks.
The ONLY RULE to keep it fresh and from falling apart
Now comes the "hot take" and it is this: the convertibility between different currencies should be non-existent or highly limited. This is to prevent a single exchange rate from becoming dominant in the chain (as happens with the Gold Piece in most TTRPGs). Currencies should differ not only in value but in ENDS. If you have a currency that can replace or is more effective than the others, it will inevitably overshadow them. Acquiring treasures valued in gold should feel vastly different in tone and obstacles from acquiring those valued in copper.
Always keep in mind that when applying these divisions between currencies, the goal is for each one to tell a different story, be associated with a specific group, and, above all, ensure that acquiring that currency is an adventure in itself.
One last point to make: As the title states, this post is only focused on PHYSICAL goods that can be exchanged for other goods (tangible or intangible). The use of reputation, coercion, favors, or quests to obtain other goods is not covered by this post (perhaps in a future one?).