HotelDruid is an excxellent Open Source package for hotel rooms management or weekly and daily rental of apartments developed by Marco Maria Francesco De Santis under a GNU Affero General Public License.
We like it because it allows us to segregate the management of the hotel or apartments from the front end presentation of the premises to potential holidaymakers/tenants when we are developing for our own clients.
As we have mentioned before HotelDruid is not intended to be the front end for any hotel or other holiday accommodation website. Our own preference is to use the Joomla Content Management System(CMS) to fulfil this function. There are many extra extensions available for this to 'spice up' your clients website.
The HotelDruid availability check is the primary means of a potential customer interacting with the software. Marco has achieved this by presenting a template which is highly customisable from the HotelDruid back end which can then be included in other front end sofftware as an iframe.