Appointment Booking Calendar - With the Appointment Booking Calendar you can accept online bookings from a set of available time-slots in the calendar.
Booked Scheduler - Booked (formerly phpScheduleIt) is a simple but powerful reserve-anything scheduler.
Dudle - Dudle is an online scheduling application, which is free and open source.
ADE - Resource management and constrained activity scheduling.
Pulse 24/7 - Booking & scheduling mobile app for service providers
QReserve - QReserve is a powerful resource booking, lending, showcasing, and reporting platform.