Best Open Source Alternatives to Fastmail Calendar

Compare the best free and open-source alternatives to Fastmail Calendar — self-hosted and desktop replacements you fully control, ranked by GitHub stars, license and platform support.

Curated by open-source.store · Updated August 2026 · 6 alternatives

Fastmail Calendar

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Platformsweb, mobile, ios, android

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Fastmail Calendar alternatives compared

Open-source alternatives to Fastmail Calendar, compared by stars, license and platform
Tool		License	Platforms	Self-hosted
Cal.com	47,171	AGPL-3.0	WebDockerLinuxmacOS	Yes	Jul 2026	Visit
Radicale	4,864	GPL-3.0	LinuxmacOSWindowsDocker	Yes	Aug 2026	Visit
Baïkal	3,253	GPL-3.0	LinuxDockerWeb	Yes	Jul 2026	Visit
SOGo	2,140	GPL-2.0	LinuxDocker	Yes	Jul 2026	Visit
DAViCal	0	GPL-2.0	Linux	Yes	—	Visit
InfCloud	0	AGPL-3.0	Web	Yes	—	Visit

Top open-source Fastmail Calendar alternatives

Cal.com47,171AGPL-3.0

An open-source scheduling infrastructure and booking platform.

WebDockerLinuxmacOSWindows

vs Fastmail Calendar: a free, open-source option you fully control, licensed AGPL-3.0.

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Radicale4,864GPL-3.0

A simple CalDAV and CardDAV server for sharing calendars and contacts.

LinuxmacOSWindowsDocker

vs Fastmail Calendar: a free, open-source option you fully control, licensed GPL-3.0.

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Baïkal3,253GPL-3.0

A lightweight CalDAV and CardDAV server for managing calendars and address books.

LinuxDockerWeb

vs Fastmail Calendar: a free, open-source option you fully control, licensed GPL-3.0.

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SOGo2,140GPL-2.0

A collaborative groupware server with a focus on usability, sharing CalDAV and CardDAV.

LinuxDocker

vs Fastmail Calendar: a free, open-source option you fully control, licensed GPL-2.0.

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DAViCal0GPL-2.0

A CalDAV server written in PHP for shared calendar and contact management.

Linux

vs Fastmail Calendar: a free, open-source option you fully control, licensed GPL-2.0.

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Best Open Source Alternatives to Fastmail Calendar

Fastmail Calendar

Fastmail Calendar alternatives compared

Top open-source Fastmail Calendar alternatives

More alternatives to Fastmail Calendar

InfCloud