the Unbound Sky
Few Planes are known to the scholars of the Unbound Sky. These other worlds are:
The Elemental Planes of Air, Earth, Fire and Water;
the Planes of Law and of Chaos, which may in fact be several planes, each;
the Plane of Shadow;
and the Unbound Sky, for all intents and purposes the Prime Material Plane.
Spells and other magics which state interaction with the ethereal plane or astral plane are actually interacting with the Plane of Shadow, the only transitory plane in this cosmology.
Other planes are postulated- a Plane of Dreams, a Plane of Life, and a Plane where the Unnamed God originated, before creating himself into the Unbound Sky.