Currency

Different regions of Discworld use different currencies. All shops, banks and services operate in local currency only.

You can get the list of currencies and coin values in game with command "help currency"

If you want to pay for something somewhere, and don't have local currency, you have different choices. Simplest is to change money in money changer. It is not recommended, because rates are always very unfair.

Other option is to change money, using a bank - deposit money in one branch with currency you have,and withdraw in other with currency you are going to spend. You can convert between Ankh-Morpork, Lancre and Djelibeybi money, or from AM to Agatean Empire with only 1-4% comission. converting from Agatean or from/to Genuanis not that easy.

Ideal solution is to avoid converting money at all. For example, you can pay for house rent, club, family, advancement in guild in any currency (if you have a branch of your guild in that region). Also, you can consider learning the art of stealing, so you can "buy" things without money, or paying with money of nearest NPC(s) :)

There are a number of player-built online currency converters.

One of these is on Simidhel's site.

Provincial

Provincial money were widespread in the past, but now you can find them only in some obscure places. Also, one of AM money changers still accept this currency. Brass provincial coin is used as a base for expression value of all other coins.

Ankh-Morpork

Most popular currency, used in Ankh-Morpork itself, Sto Lat and surroundings.

Most notable coin is Royal - Pishe accept only this coins as payment for lives.

Djelibeybi

It is used in Djelibeybi... And that's about all.

Genua

There are no coins between cent and livre, and if you "take money from corpse" a lot while in Genua, you'll be burdened by pounds of cents in no time.

Lancre

Most confusing money system on Disc. Used in a lot of towns and villages, from Ohulan Cutash to Escrow.

Agatean Empire

Currency of second biggest city in Discworld MUD - Bes Pelargic. It is hard to convert money from this currency to dollars, so better options is to use them for things that you can pay in any currency - advancing in guild, family and club upkeep, house rent (for latter use Dancing Tiger bank)

Ephebe

Currency of not-yet-implemented Ephebe. Nevertheless, you'll see a lot of Ephebe coins if you'll check sailor's purses in Djb or OC docks.

Other currencies

Virtually non-existant, except Pumpkin coins, which are currency of newbie area.