I've been hooked on for quite some time now a couple of online "diary" stories/books. I love them both. They are both about the "Zombie Apocalypse" but they each have their own unique storylines and ideas.
The first one has been going on for a year and a half and it extremely addicting.
The 2nd one will be having an entry in a couple of weeks with two "walk on" guest characters that die horrible and gruesome deaths. I will be one of them! The first two books are available on Amazon for like $2.99 or some time. But they offer some sample chapters on the website to see if you like it before you buy it. But the 3rd book is finished and completely online until it is edited and made to put up on Amazon. The 4th book is still being written so you can read it as he inputs it.
Here's the links to both:
Adrian's Undead Diary:
What Zombies Fear: