Dudle - Dudle is an online scheduling application, which is free and open source.
Kin Calendar - The simple and connected calendar
Appointment Booking Calendar - With the Appointment Booking Calendar you can accept online bookings from a set of available time-slots in the calendar.
Google Calendar - Spend less time managing your day & more time enjoying it
Pulse 24/7 - Booking & scheduling mobile app for service providers
Teamup Calendar - Cloud-based calendaring using capability URL, application developed in Zurich, Switzerland.