Demigod

Demigods, were considered the first rung on the ladder of the gods. Demigods were true immortal deities and capable of granting spells A demigod typically had only a handful of clerics and roughly 300 to 3,000 worshipers that typically prayed to a deity of such power.

A demipower was a god that either had just risen to godhood, just returned from the dead, suffered a loss of divine power or shared a part of their portfolio with a god of greater power. For example Finder Wyvernspur was a mortal who rose to the rank of demipower. Moander was an example of a once powerful god who returned from the dead as a demipower. Jergal was a Greater deity at the time of Netheril but reduced himself to the level of a demipower. Both Savras and Velsharoon were demigods that shared their portfolios with gods of greater power, Azuth and Mystra.

Due to their very natures, demigods represented a very narrow and restricted ideal or aspect of existence. This meant only a certain group of mortals would consider the demigod suitable for worship, until either the ideals that the demigod embodied become more popular or the demigod was given or took the portfolios of other deities.

Demigod Abilities
A demigod could create and control a small realm (generally within one of the Outer Planes) that could be shaped and controlled as the demigod wished. Additionally, the demigod had a small ability to shape reality in regard to his or her portfolio as it related to mortal life, become extraordinary in some skill related to his or her portfolio, and extend his or her senses to a mile away from an avatar or any holy sites dedicated to him or her.

Faerûnian Demigods

 * Deep Duerra
 * Finder Wyvernspur
 * Garagos
 * Gargauth
 * Gwaeron Windstrom
 * Haela Brightaxe
 * Hoar
 * Jergal
 * Kiaransalee
 * Laogzed
 * Lurue
 * Nobanion
 * Red Knight
 * Savras
 * Sebek
 * Selvetarm
 * Sharess
 * Shiallia
 * Siamorphe
 * Ulutiu
 * Valkur
 * Vaprak
 * Velsharoon
 * Drasek Riven

Demigod Discombobulation
In every edition of D&D except 4th, demigods have been the lowest rank of power of the divine god scale. They are true gods, just the weakest of the true gods. In 3rd edition this was represented by them having a divine rank of 1 to 5. They could grant spells and do anything a god could do, just of a lesser power then other more powerful gods.

4th edition brought in the idea of exarchs and calls them demigods, but does not offer much explanation of what they are. Exarchs are just another term for demigods.