I have several.

The Conspiracy diary, gives details about the intention of everyone and their connections, however there are many actual links and stories being told by the diary, some of which true, most of which false.

The Medical Diary, owned by a doctor, can see the health hazards of anyone on his patient list.

The operational diary, owned by some army or police guy, can predict the movements of people in a building he has to storm, etc.

The Lover Manager diary, can declare someone to be that girl's boyfriend or girlfriend, will see all interaction of this person relating to either you or the other boyfriends/girlfriends (Something like a 3 limit), useful for managing a complex love life, or your nemesis.