Here is the link to the explanation. There you will find some cool artwork, a group read challenge (including The Graveyard Book by Neil Gaiman), and lots of links to blogs that are participating.
Acceptable genres include Mystery, Suspense, Dark Fantasy, Gothic, Horror ... but really anything that you think works. The rules are very flexible, which is good because I'm a bit limited by what I can find for free on my Kindle this year.
Some potential candidates, but suggestions are always welcome:
1. Rosemary's Baby by Ira Levin
2. The Damned by Algernon Blackwood
3. Off Season by Jack Ketchum
The other one I'll do is Peril the Short Story. I'm not actually a big short story fan. But I recently found a few books of modern Lovecraftian fiction, so I'm going to work through those. Though who knows what else I might find.