Akara: Lands of Chaos
Arcane magic works much as one would expect, with one vital variation. After the events of the Worldrift, some stuff of Chaos seeped into the land. This has left various places rife with the chaotic energies of an alternate dimension. The Chaos Zones wreak havoc on static magic, and will cause magic to go awry.
The gods are imprisoned, but they are not dead. This means that divine magic still works, though the clerics of the world feel their power as if from a far off place. The faith of the people is slipping, and who knows the effect this may have on the gods and their priesthoods. It is said that without the faith of mortal souls, the gods themselves will die.
Cosmology of Akara, or an Encyclopædia of the Planes
The wizards of old quickly found a way to travel between this realm and others. Thus, a cosmology was soon produced. The Prime Material plane, in which the lives of most mortals take place, is immediately and coterminously bordered by the Ethereal and Shadow planes. Arranged about these, coterminous with the Ethereal and Shadow planes are the other planes. It is therefore possible to travel to any realm via either the Ethereal Plane or the Plane of Shadow. It is through the Plane of Chaos that the Old Gods entered the world.
The cosmology of Akara is identical to the standard cosmology found in the DMG 3.5