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.
Dotcal - Personalized booking pages for absolutely everyone
Easy! Appointments - Open Source Appointment Scheduler
Timezo - Share events with the correct timezone