Scheduling looks simple until you add time zones, calendar sync and payments. These projects handle the hard parts and let you keep booking data on your own servers.
1
cal.diy calcom/cal.diy
Scheduling infrastructure from the Cal.com team: booking pages, team routing and calendar integrations. The best-known open-source answer to Calendly.
2
rallly lukevella/rallly
Group scheduling polls: share a link, everyone marks the times that suit them. Replaces Doodle more than Calendly.
3
easyappointments alextselegidis/easyappointments
Appointment booking for services (clinics, salons, consultants) with providers, services and working hours. GPL-3.0.
How to choose
One-to-one meeting links like Calendly: Cal.com. Finding a time for a group: Rallly. A business that books customers into services: Easy!Appointments.
How we pick: we start from every public GitHub repository with 1,000+ stars, keep the projects that do the job in the title, and read their descriptions and licenses. Stars show community size, not quality, so we also show maintenance status. Nobody paid to be listed.