Online Booking System to add to xhtml website

This project is for adding an online booking system to an existing xhtml website. The booking system needs to allow visitors to view empty slots the site owner has and book for an available time. There will be a few different types of appointment of vary length and availability. It needs to be able to sync with google calendar. The owner needs to be able to view the detail as well as being able to override it. The successful applicant will have worked on a similar project and be able to show a demo prior to winning the bid. The resulting system needs to be installed successfully onto the current xhtml site or convert the current site into a different format, cms or php.