Rant, and the Poisonwood Bible?

In the novel Rant, it is an oral biography where different characters speak and tell the story. The Poisonwood Bible is similar in that all characters speak independently of each other and tell what is going on in the novel. You learn what happens by reading each individual's part in the novel. like a diary or something. i was just wondering what this is called?Rant, and the Poisonwood Bible?
I remembered that this style was used in Bram Stoker's ';Dracula,'; so I searched it and learned that, ';structurally, it is an epistolary novel, that is, told as a series of diary letters.';