Kain Darkwind's Savage Tide
What follows below is an attempt to catalog the known alternate realities that exist coterminous with Terra.
Little is known about this world. However, Heinrick Prime on this world has embarked on a murderous quest to slay his duplicates in other dimensions.
This world is characterized by a massive influx of magic. Even the most ignorant farmer possesses some small talent at spellcraft on this world. This world resembles Earth more closely than Oerth.
This world was characterized by an absence of magic, though its tales pervade the world.
This world was destroyed when a group of children ruined the sacrificial process that appeased the Inconnu.
Oerth is the name for Terra utilized by those on the Oerik continent and nearby landmasses.
Uerth is similar to Earth, except that magic exists in the shadows, subtly influencing its course. (Uerth is very likely the world Harry Dresden lives in.)
Yarth is less magical than Oerth (Terra), and as a result its history has been very different. While there have been a fair number of necromancers and even liches in Yarth’s history, these fell mages have never ruled nations. Yarth is a place for warriors and clever rogues, and it is these that have determined the world’s history more than anything.
The Dark World appears to be a close mirror of Terra. However, nearly all events seem to unfold in a grim, macabre or depressing manner. If Terra is a world of heroes and villains, the Dark World is a world of villains and antiheroes.
The Light World is a hypothetical logical counterpoint to the Dark World. Events would unfold in the most rewarding and happy manner here. If Terra is a world of heroes and villains, the Light World is a world of heroes and misguided villains who can be redeemed.