EverQuest Online Adventures: Frontiers added another playable race, the Ogre, and character class Alchemist, as well as many quests and items. The level cap was raised from 50 to 60.
Also added was the continent of Odus and a newly-opened territory of Tunaria known as Rathe Mountains, as well as high-level raid-specific zones in other locations including Plane of Sky, Lavastorm Mountains, and a subset of the Plane of Disease known as Last Home. Certain portions of Tunaria itself that existed previous to the release of EQOA: Frontiers were also revamped for higher-level players given the increase in the level cap.
Frontiers also added an alternate form of advancement by allowing players to dedicate a percentage of the experience points they received to obtaining Class Masteries (CMs). These CMs allow players to increase their power and gain new abilities. They also can purchase Master Classes with (CMs), further strengthening themselves in their area of combat. 1500 CMs is the max at level 60, a player with less than 1000 CMs can be very weak compared to one with more than 1000 CMs. 500 CMs are required to unlock a Master Class and 200 more are required to buy a Master class. A Master Class changes the Class of the player character to a more specialized "Master Class" of the original Class of that player character. An example of this is when a Wizard becomes a Sorcerer Master Class.
Source: Wikipedia, "EverQuest Online Adventures: Frontiers", available under the CC-BY-SA License.