Short answers, pulled from the story.
The Eberron tabletop role-playing game setting was officially released in June 2004 with the Eberron Campaign Setting hardback book. This release won the Origins Award for Best Roleplaying Game Supplement of 2004.
Keith Baker created the Eberron world and entered the Fantasy Setting Search competition in 2002 with a one-page concept. The project moved from a contest entry to a fully fleshed-out world bible after Bill Slavicsek suggested the name Eberron during meetings in Seattle.
The Last War was a vast destructive conflict fought between the Five Nations that ended with the Treaty of Thronehold. The war left the continent of Khorvaire scarred and unstable, creating the Mournland region where the city of Grayhold was destroyed.
The three progenitor wyrms in the Eberron creation myth are Siberys the Dragon Above, Eberron the Dragon Between, and Khyber the Dragon Below. Siberys became the planetary rings, Eberron became the world itself, and Khyber became the dark underworld known as the Dragon Below.
The Eberron setting introduces the Kalashtar, a race of psionic people descended from human monks possessed by Quori, and the Warforged, sentient constructs made of stone, wood, and metal. The Warforged were created by House Cannith to serve as soldiers during the Last War and were granted freedom when the conflict concluded.