Eberron

Eberon is one of the newer world added during 3E D&D. It is a world of technology fueled by magic. The world itself is simply known as Eberron, a large planet with at least 5 known continants, and its underdark area is known as khyber. There are twelve moons (Daanui, Dal Quor, Dolurrh, Fenia, Irian, Kythri, Lammania, Mabar, Risia, Shavarath, Thalanis, Xorlat) that orbit around the planet, as well as a rather unique feature known as the Ring of Siberys. The Ring of Siberys itself is a golden ring of particles that orbit the planet, and is the source to many of the dragon shards. One unique feature of the world is the dragonmarks and dragonshards, that seem to tap into the primordial powers of the world. The moons themselves also play a signficant role, for each moon is named after one of the many planes that the world is closely connected to.
Every so often some of the planes bleed onto the world, and these can often be told through the orbit and phases of the many moons.

The deities worshipped on the world by most races are either of the small pantheon of the Sovereign Host or the the Dark Six. Besides these two major pantheons, there are a number of cults that many ascribe to; the Silver Flame, Blood of Vol, Undying Court, and the Path of Light. Many of the races of Eberron are found throughout the multiverse, but there are some that seem to be unique to this world. The Warforged (a group of sentient constructs), Shifters individuals with lycanthrope ancestors, changelings (individuals with doppleganger ancestry), and the Kalashtar (individuals that are host to entities from the plane of dreams). It is also important to mention that the Drow of this world are not beholden to Llolth, but have assumed a scorpion theme in place with one of the Dark Six.
 
Each of the continents are host to many of the races of the world. Khovaire by many is considered one of the most active continents as it is a mix of various peoples and beings. This land is has recovered from a great war in which the Warforged were the product from. Xen'drik is a wild continent which once hosted the great kingdom of giants. It has become overrun with the Drow who prowl its ruins. Sarlona is cradle of civilization. Currently the the Dal Quor, and many psionic beings make this land their home. The Argonnessen continent is the home of the dragons, much of the land unexplored. The northern icecap is where the Frostfell is, an icy wasteland. There is also the sub-continent of Aerenal, which is the ancestral home of the elves and home to the Undying Court.

One of the unique features of the world are Dragonmarks. Odd magical birthmarks that appears on certain individuals and great special powers. So far there are at least 12 unique varieties catalogued, each grouped to a clan.