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Best API Calendar & Contacts for self-hosting

The 5 best API calendar & contacts you can self-host, ranked by community traction.

Open Event Server

Calendar & Contacts

Self-hosted event management and ticketing backend

Replaces Eventbrite, Sched

★ 3k Hard setup GPL-3.0

ETAR

Calendar & Contacts

Open-source calendar server companion for events

Replaces Google Calendar

★ 2.6k Medium setup GPL-3.0

OpenCalendar Sync

Calendar & Contacts

Self-hosted shared calendar with public event pages

Replaces Calendly, Google Calendar

★ 852 Medium setup MIT

Nextcloud Tasks

Calendar & Contacts

CalDAV task list app for Nextcloud

Replaces Google Tasks, Todoist

★ 701 Easy setup AGPL-3.0

Thunderbird Appointment

Calendar & Contacts

Self-hostable scheduling tool for booking meetings

Replaces Calendly, Doodle

★ 547 Medium setup MPL-2.0

Every option here is open-source and self-hostable, tagged API within the calendar & contacts category. Compare them on the individual app pages for setup difficulty and resource requirements.