Brave New World
Elementals have long been harnessed to power magical devices. It was only several hundred years ago, however, that an enterprising mage realized that the same magics which could be used to summon golems and elementals could also call forth those devices, if properly attuned. A master arcane smith, he created a small fleet of ground and astral vehicles and hired out a small guild of mages as couriers. It was not until his death, when his heirs sold his company and his process to a subsidiary of Planescapes Inc that Mechromancy truly took off.
Planescapes Inc and its subsidiaries had the resources to quickly expand the stock of elementally powered vehicles hundreds of thousands of times over. Rather than hire out trained mages to perform and maintain the summoning, Planescapes’ arcane engineers subdivided the process into dozens of low-energy sub-summon spells, then bound them to cheap, disposable spell-trigger items. The end result were mass-produced Mechromanic Charms, single use items which could summon an elemental vehicle for a limited time, available to the public for a minimal cost.
Planescapes Inc guards its spell process jealously, and though corporate espionage is always a threat they have so far been fairly successful in maintaining their monopoly on Mechromancy. Nevertheless, a small number of pirate vessels are known to exist, bound to Mechromantic Charms which do not become discharged after a single use. The possession of such pirated charms is strictly forbidden within Sigil and the Outlands, but the Astral Sea is not subject to the laws of plane.