One of the four planets formed when the Sartan sundered the Earth into four elemental realms in The Death Gate Cycle books by Margaret Weis and Tracy Hickman.
Arianus is the realm of air, comprised of islands that hover on different levels above a perpetual storm known as The Maelstrom. The islands are made of Coralite, and are lighter than air because of the natural gaseous emissions of the coral-producing animals. The islands were originally configured like stepping stones over the storm, but eventually drifted apart. Water is scarce in most of Arianus, leading to the currency being based on barrels of water and maintaining an intense power struggle over who will control the supply. The land is made up of three sections.
The uppermost islands are known as Terrel Fen and were populated by the human wizards (Mysteriarchs) until the magic which made them inhabitable failed. Eventually the atmosphere became un-breathable, and the wizards moved down to the mid realm. The mid realm is populated by both elves (known as welves to the dwarves) and humans. The two races live on separate islands, and are very distrustful of each other, due to the elves using human slaves, and differences in technologies (elves use magic, humans in this realm cannot) and politics. The human political system is based on a monarchy, while the elves’ system is an empire.
The low realm (Drevlin) is plagued by the storms of The Maelstrom, and home to a giant machine called the Kicksey Winsey. The great machine is worshipped by the inhabitants of this realm, the dwarves (who call themselves gegs), though they don’t know what the machine is supposed to do. They spend their lives maintaining the machine, and providing water to the elves who give the gegs “treasure” (garbage) in return. The gegs consider the elves gods. Though they are sitting on all of the wealth of Arianus, they are simple people who frown on curiosity of any kind, so don’t understand what they are doing and why they do it.
The function of the Kicksey Winsey was many-fold. The great machine was controlled by a metal golem who sent power and instructions to each part of the machine, as needed. The dwarves made sure that each individual section of the machine was in working order. The machine was self expanding, and, using raw materials from the realms, produced everything the dwarves might need in everyday life. It also aligned the floating islands and delivered water to the upper realms. It was powered using energy from Pryan, but when the Death Gate was closed, the power was cut off, and the machine became slow and disoriented, expanding without direction, and cutting off the water supply to the other races.
All of the Sartan on Arianus died out (possibly due to the practice of necromancy on Abarrach), leaving the three races to govern themselves, and the realm of air to fall into chaos.
Information taken from the novels themselves, and a summary at http://members.iquest.net/~jschatte/novels.html