Fallout 3/Factions

The family
The family is a cannibalistic group located near Arefu, lead by a person who believes their normal cannibalistic nature causes them to be barbaric savages. The family created a set of five laws to ritualize and control their tendencies.

Church of Atom
The church of Atom worships the bomb located in Megaton.

Hunters
Not a faction per se, but they collect meat from animals from around the wasteland.