Citizens of Stem City request goods that their businesses require from several Nexus outposts scattered across the city. These purchased goods can be building materials, food, technology, or anything else that off-worlds are willing to give Stem City. The investors digitally pay Stem Tower with Markcards for these goods. The desired materials are then taken from the Nexus' reserves and shipped to their enlisted residence shortly after. That's how the internal city economy works.
The external economy is more complicated.
The Grand Shroom's stems stretch out across Stem Island. As the stems droop off the edges, glowing green portals form at their tips. These portals actually work as wormholes to another dimension, which alien visitors inconsistently refer to as either the galaxy or the universe. These wormholes are a powerful tool for off-world empires and companies to cut both cargo and passenger travel times by months.
Stem Tower has strict rules about who can use these wormholes. Anything that enters through a Stemrail portal that isn't one of the Nexus' specially designed trains is to be destroyed by armed Lawair units.
Stem City only allows for these off-worlder civilizations to impede on its extradimensional turf via detailed contracts. Many of Stem City's stockpiled supplies come from these lucrative agreements. For every train that these groups use, Stem City must be paid in some fashion. In exchange, these external groups are welcome to load cargo and passengers into any wormhole willing to accept them.
If Stem City requires something that one of its partners is not actively trading, the Nexus' management is authorized to use its or The Complex's Marks gold reserves to pay. Gold is precious no matter where you go in the multiverse.
Stemrails refer to a pair of two suspended, electricity-powered tracks that travel up and down every single major stem. Each track has a comfortable docking station on the other side of the wormhole. Trains can be a dozen cars long. Each standard cargo vessel usually has a crew of three engineers aboard along with a squad of a dozen Lawmen. Passenger trains usually carry crews of up to two dozen. Most of these jobs aren't actually filled by Stem City-born citizens; rather, they are mostly off-world companies hiring their own manpower.
Passenger trains are mostly used to allow people to venture into Stem City for tourism. Incoming visitors are given special Markcards that allow them to spend a certain amount of the state's spending. Tourists aren't allowed to leave the walls of Stem City. A majority of tourists flood in during the one weekend per month that Mistress Gwino performs.
The safest method of Stemrail raiding—the crime of raiding incoming Stemrails for their cargo— is the simple act of cutting the electricity from a specific portion of the rails for a short period of time.