Non-class skill books are expert skill books which any class can use. Although, unlike ordinary expert skill books, these skill books can not be upgraded. Most of them grant only small improvements but few of them are actually quite powerful. At the moment, there are 44 non-class skill books, 41 of which are passive and three that are active. The only requirements to use these books are a character level of 18 and an empty combat kit slot which means that these books won't consume the space mean