I don't think Ruminations of the Elder Scrolls is unique.
This list doesn't included journals or notes; only books.
Atlas of Dragons.
Holdings of Jarl Gjalund.
Annals of the Dragonguard.
Signed Copy of Uncommon Taste.
Wind and Sand.
Words of the Wind.
Confessions of a Khajit Fur Trader.
Diary of Faire Agarwen.
Journal of Mirtil Angoth.
Nchunak's Fire and Faith.
Night of Tears.
Notes on Dimhollow Crypt v3.
Notes on Yngol Barrow.
Notes on the Lunar Forge.
Power of the Elements.
Saint Jiub's Opus.
The Betrayed.
The Book of Fate.
The Dreamstride.
The Four Totems of Volskygge.
The Two Nightingale Books.
The Nirnroot Missive.
The Secrets of Ragnvald.
Touching the Sky.