Cron - Cron Calendar.
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.
zcal - zcal is the fastest way to schedule every meeting for Free and make it personal.
Acuity Scheduling - Automate your client bookings, cancellations, reminders & payments using the worlds friendliest online scheduling software.
Cal.com - Cal.com (formerly Calendso) is the open source Calendly alternative.
Reservio - Reservio is a simple online booking and appointment scheduling application.