Task Coach - Task Coach is a simple open source todo manager to keep track of personal tasks and todo lists.
Acuity Scheduling - Automate your client bookings, cancellations, reminders & payments using the worlds friendliest online scheduling software.
EssentialPIM - EssentialPIM is a free Personal Information Manager that keeps up with the times and lets you manage appointments, tasks, notes, contacts, password entries and email messages across multiple devices and cloud applications.
Calendly - Say goodbye to phone and email tag for finding the perfect meeting time with Calendly. It's 100% free, super easy to use and you'll love our customer service.
Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.
Reservio - Reservio is a simple online booking and appointment scheduling application.