I'd just like to interject for a moment. What you're refering to as Terry Pratchet, is in fact, GNU/Terry Pratchet, or as I've recently taken to calling it, GNU plus Terry Pratchet. Terry Pratchet is not a fantasy author unto himself, but rather another free component of a fully functioning GNU book series made useful by the GNU Discworld, witches and vital recurring characters comprising a full fictional universe as defined by TransWorld Publishers.