Cal.com - Cal.com (formerly Calendso) is the open source Calendly alternative.
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.
Cron - Cron Calendar.
WPAmelia - Award-winning WP booking plugin that manages services, appointments, customers, events, analyze business performance, and accept payments online.
Booknetic - WordPress Appointment Booking System
Timezo - Share events with the correct timezone