Also known as the Future Diary:
High school 2nd year, Amano Yukiteru, is a boy who has problem making friends. He thinks of himself as a bystander and will always write down everything he sees in a cell phone diary.

Tormented by solitude, Yukiteru began to imagine things like a friend called Deus X Makina who is apparently the Lord of Time & Space. Seeing Yukiteru's miserable state, Deus gives him a new ability. His diary will now record events that will happen in the near future. Yukiteru is then forced to participate in a game which the winner will become Deus's successor.
The manga is really amazing. If you haven't read it you should. It's like a cross between Death Note and Battle Royale somewhat and the theme is quite unique. After I read first 1 or 2 chapters, I was hungering for more and more.

There's currently around 20 chapters scanlated, though there are missing chapters not known by mangaupdates they're up there on Lurk. Git! Go read this! You won't be disappointed if you're into psychological thrillers.