Dungeons & Dragons, if you follow its basic logic, assumes lots and lots of gold is present in the world. No, more than that. Nope, higher. Gold coins are the basic economic unit, and weigh 1/10th of a pound (45.4 grams). Think of a silver dollar, which is 1 troy ounce (31.1 grams). Now, add 50% more weight and make it 3/4ths as thick, due to the relative density of gold and silver. That's the D&D gold piece.
Most clones don't fiddle much with the basic monetary system. Adventurer Conqueror King makes the gold piece 1/1000th of 1 stone. This is actually a bit light in "real" stone (14 lbs), but because ACKS assumes 1 stone is roughly equal to 10 lbs, this gives 4.54 grams per gold piece. That's equal to the Roman denarii pictured above, or the late Roman solidus that was the basis for gold coins for most of the Middle Ages. But it's still a gold-based economy, even if the gold requirements are significantly lower.
Lamentations of the Flame Princess switches to a silver standard, and gives 1 XP per silver piece. Silver pieces are 1/50th of a gold piece, which is probably a better approximation than 1/10th or 1/20th, although prices fluctuated drastically in history. It also eschews odd metals like platinum and electrum, to its credit. But it doesn't get weight very precise; the encumbrance system is kind of abstract, and 100 coins are an encumbrance unit. I would still
LotFP's silver standard has a lot of appeal for me, because it makes a chest of gold absolutely phenomenal. 40 GP? In a gold standard that's a rounding error, but in LotFP it's enough to get a fighter to second level. Even a few gold pieces are worth a lot more risk relative to the reward.
And at the same time I like to geek out a bit over ancient silver coins, which is heavily supported by a silver standard. They aren't just an encumbrance penalty to the PCs who have to haul them back, or loose change that get stuck between the couch cushions, but the basic unit of economic value that the PCs have to deal with. Even copper pieces aren't worthless: the infamous 2000 CP of Dwimmermount are worth 200 XP in LotFP.
By making gold extremely valuable and rare, the silver standard also lets you use different metals, like bronze or brass, and have some interesting variables in your coinage. Relative values can be fixed at various rates. Electrum (a gold/silver alloy) coinage was extremely rare, and platinum as a metal was unheard of until the 1500s. Billon was frequently used, famously in the gradual debasement of Roman silver coinage to bronze (the antoninianus or "double denarius" was the coin most associated with this).
Overall, I think that a hybrid of the ideas that find expression in LotFP and ACKS provide the best solution for coinage: the values from LotFP (1 GP = 50 SP = 500 CP) and the weights from ACKS (100 coins = 1 pound). It makes the denarius the model coin, as it should be.
