Fictitious databases in video games.

The Armored Core Series has always been a favorite of mine, as the the whole menu system makes you feel as though you are in some control area ready to accept missions for certain areas/corporations, and the emails you receive from opposing pilots make you feel a part of it.

When it's done right I like it, but I couldn't get into the FFesque ones as they made me feel "out of the game" rather than more emmersed in it.

Another type that isn't mentioned is the "lore books" in some games, like Oblivion/Morrowind, both of which had extensive lore books just on the history of the world. Those I liked, and many were quite interesting to read. I can see many mods that could come out of those kind of things.

Jam it back in, in the dark.