A public bookcase (also known as a free library or book swap or street library or sidewalk library) is a cabinet which may be freely and anonymously used for the exchange and storage of books without the administrative rigor associated with formal libraries. When in public places these cabinets are of a robust and weatherproof design which are available at all times. However, cabinets installed in public or commercial buildings may be simple, unmodified book-shelves and may only be available during certain periods.