These books are all difficult to find, and though most are not magical, they all contain knowledge that adventurers could put to use.
The Histories of the Ancients
This is a scholarly work written in BY 1322 about the pre-Imperial cultures found on the continent of Toutus. Chapters include the Lengkar Theocracy, the shortlived Republic of Jaroketh, demihuman clans and cultures and even one on large and stable non-human societes such as as the Turrokoth Despotship of hobgoblins. The work, although highly praised at the time, is not entirely accurate, and is a mixture of sensible academic study, plagiarism from other works and artistic license. Nonetheless, it does point to a number of specific ancient ruins dotted around the continent that are far older than the more recently destroyed cities from the wars and the Summoning, and suggests where further ruins might lie undiscovered.
The Abominable Cults of Chaos Worshippers
Commissioned 50 years before the start of the Wars between the Empires (BY 1511) this is a guide for lawful clerics and righteous investigators to detect, track down and destroy chaos cultists, especially those lurking within civilised society. It gives a reasonably accurate description of different cults including their aims, activities, recruitment and how they try to remain hidden. A lot of what is written here is still true 100 years later, and adventurer reading this may gain valuable clues and insights when dealing with Chaos cults.
Travels Under a Blood Red Sky
This book is banned by some lawful folk, while others advise great caution in reading it. Written by the mad archmage Androsomus, it describes his travels around the Planes of Chaos, including Hestoris, Urdonor and Aegothis. The book gives advice on surviving these malevolent realms and also includes some magic-user spells for travelling to these planes.
More controversially it talks extensively about demons, both as adversaries and as potentially useful creatures. It describes Androsomus' attempts to command and control demons while on the Planes of Chaos and on the Material plane.
The Papyri of Zoth
These bundles of ancient crumbling sheets are unique, and are believed to be in the hands of a private collector who fled the capital with her collection during the Summoning. These papyri are at least 2000 years old themselves, but they speak of a great and terrible civilization called Zoth from way before the rise of the Empires of Toutus, Bellenos or Bursia. The exact location of Zoth is not certain, but it seems that they gave rise to the Cynideans (the remains of whom are found dotted around the Tekhumis region) and the Lengkar Theocracy (in eastern Toutus, mentioned in other books) and possibly even the Telthus Empire. This would be dry academic theory, were it not for the descriptions of some of the spells inscribed on the walls of the ruins of Zoth. The Papyri do not contain the spells themselves, but talk of mages of Zoth wielding incredible powers. Any wizard would give his right arm and all his treasure just to know where these spells are engraved.
Magic Weapons I Have Known and Loved by Snorrvord the Elder
Written in the dwarven language and in dwarven runes, this book is a catalogue of nearly a hundred weapons of different enchantments and potencies that the blacksmith-cleric Snorrvord the Elder had either personally made or had come across during his travels (which spanned 300 years). Although originally from the Confederacy of the Ten Peaks, Snorrvord visited dozens of dwarven settlements and strongholds around Toutus. He often wrote about the methods and techniques of weaponmaking and blacksmithing, including case-studies of particular weapons. Also included are the weapons' initial owners, and where they might have been or where the weapons ended up around the book's completion (BY1456).
The Noble Families of Toutus
Genealogy is of little interest to adventurers, but to those who believe they are of noble descent this book is considered the definitive reference to who is entitled to which seats of power. The book also talks about heraldry and coats of arms, etiquette and protocol, as well as brief biographies of great or infamous Toutatian nobles. Only five copies of this book were produced by the office of the Imperial Herald BY1551, just as the Wars between the Empires were getting serious, and it was intended to be used by the Herald to help him sort out claims and counterclaims after the war. Even though the Toutus Empire has collapsed, some surviving nobles or would-be nobles are desperate to prove their claims are true - and a few seek to hide or destroy the book that would show them to be usurpers or frauds.