The Boston Book Festival on Saturday, Oct. 27, in Copley Square is not just about the reading or buying of books. The fair will also have 125 presenters, sessions for kids and adults including keynote speakers Lemony Snicket and Richard Ford, a street fair, workshops and live music from Berklee College of Music students. The best part is that New England’s largest literary event is free. The festival’s most ambitious event is called “One City One Story.” The citywide distribution of a short story culminates in discussion around the city’s libraries and a writing prompt. Copies are available online, at all branches of Boston Public Library and at certain city events.