In Development Game
Planes occur naturally in groups of seven; these are called daeverspaces, after the mage Anatolin Daever who was the father of modern planar cosmology. Planar cosmologists also identify feremsets, groups of eight daeverspaces first postulated by Tullus Ferem.
Modern planar cosmologists believe that the material plane lies at the locus of three feremsets – one that is primarily composed of matter and energy, one that is primarily composed of thought and spirit, and one that is primarily composed of dreams and magic.
Materia – The feremset containing daeverspaces focused around matter and energy, including the four elements, the positive and negative energy plane, the material plane, and the far plane.
Anima – The feremset containing daeverspaces focused on thoughts and souls, including morality and ethics, the mindscape, and realms of the dead.
Aethera – The feremset containing daeverspaces focused on dreams and magic. It is the least understood of the three known feremsets.
Other feremsets are believed to exist, and may be reachable through other known daeverspaces; as they do not intersect the material plane, however, they are speculated to be incomprehensible to scholars of the material plane and no traveler has been encountered from one.