The Prime Material Plane

The prime material planes are at the Center of the Great Wheel. All of these Material Planes have the same type of connection to the Ethereal, the Astral, and the Outer Planes. 
There is a cluster of planes that are easily travelled between without much effort beyond the standard magic as long as its a traveller that knows such things.

All of the Cluster primes are alternate Material planes to each other but all have the exact same physics and Metaphysics. Magic differs not in power upon these planes but instead how the magic users access the source of magic. For example, the Weave is Mystra and accessing the Weave is how most arcane and divine spellcasters access the source of Magic. There are other ways to access magic within the Forgotten Realms, but very very few know of these. The differences and nuances to these methods are often what distinguishes the worlds from each other. But it seems access for most magic users are similar as many mages have travelled between these realms while keeping their magic proficiency honed.
These Primes share easy egress to Sigil the City of Doors in the Outlands and numerous gateways exist on Toril to many other planes including those outside the cluster.    

• Toril of the Forgotten Realms
• Krynn (Dragonlance)
• Aebrynis (Birthright)
• Mystara
• Athas (Dark Sun)
• Oerth (Greyhawk)
• Airdhe (Castles & Crusades)

Amongst a class of adventurers there is a prime material flow that connects these Prime Material Planes called the Phlogiston.  
The Dieties (or lack thereof) of these worlds all only have power within a particular sphere containing the world.

Manifestation

Phlogiston Flow
Gates
Moonbeam Roads