Mag-lev
From MYSTlore
The Magnetic Levitation Car, or Mag-lev was a transportation device that Gehn built on Riven. It consisted of small vehicles hanging from rails, propelled along the rails by magnetic attraction.
The necessity for Mag-levs became clear when Riven split into five islands. At first, Gehn had built bridges to connect the separating islands, but as they drifted farther apart, a new method of inter-island transportation had to be developed. The rails are built to expand as the islands drift apart, but they can only expand so far and would eventually need to be replaced.
Gehn mostly abandoned the mag-lev after he managed to create a primitive linking book by using Riven's materials. These linking books needed power to work, however, which lead to the creation of the fire marble domes littered around the islands and Great Golden Dome on Temple Island.
[edit] Background
The Mag-lev is also called a mag-car by some, including Richard Vander Wende, its designer.
Originally, the islands were going to be connected with pathways but since that would make the game less interesting, the mag-levs were written into the gameplay. The conceptual pathways were then added as a backstory: they existed before Gehn built the mag-levs.