easyReservations is a free WordPress plugin that adds useful features for receiving, managing and handling bookings easily from your WordPress site. You can use it for any reservable products like hotels, car rentals, events, B&Bs, appointments or conferences etc.
With WP Simple Booking Calendar you can show up if something is booked or available. You can use it to show if your flat is available for rent etc. The plugin is useful for those website owners who have something to rent out like a holiday home, an equipment etc etc.