Eleventh Doctor's diary
Talk about it here.
The Eleventh Doctor kept a diary of his adventures with River Song. He and River often synced diaries when they met so they knew where they were in each other's timelines. (TV: Silence in the Library, The Impossible Astronaut)
The cover was TARDIS blue and was similar to River Song's diary, but unlike River's, the cover of the Doctor's diary had three rectangular panels and a Seal of Rassilon. (TV: The Impossible Astronaut)