From the introduction:

Gods of the Dead presents four new completely open game content deities of death and undeath that can be dropped into virtually any d20-style campaign setting. Vagruth and his sons hold responsibility over all aspects of death, dying, and undeath, and their unique relationship can be added to any setting to provide plot devices or a quick back-story for your world. Instead of just providing a bunch of game mechanics to incorporate into a game, Gods of the Dead also offers you a mythology to add more depth to your fantasy setting.
Two of the deities, Vagruth and Nadru, are presented with two sets separate descriptions, allowing you to decided how you want to introduce them into your game. Is death a terrifying notice, and the god of death a malevolent force in your world? Or is death considered part of the natural order, and the god of death is an indifferent but fair being? The choice is yours.