MA Calendar

The only fully-functional open-source calendar app with Material You.GPL-3.0-only

Persian Calendar

Android Persian CalendarGPL-3.0-only

CalEF (Calendar Entry Formatter)

Create and send Appointment-Confirmation-Message from Android-Calendar-Entry.GPL-3.0-or-later

Jalali Persian Calendar

Gregorian and Persian (Jalali) calendar with a two-way date converterMIT

Hebrew Calendar

Biblical feast days, sabbaths, and moon phases on a lunar calendarGPL-3.0-only

Fitness Calendar

A private and offline by default activity tracker.GPL-2.0-only

Calendar Color

Change the calendar colorMIT

French Calendar

French Revolutionary calendar widgetGPL-3.0-only

CalSync - Local Calendar Sync

Sync local calendars offline. Free, open source, no account needed.GPL-3.0-only

CalSync - Notification Calendar Sync

Sync notification time info to calendar automaticallyGPL-3.0-or-later

Birthday Calendar

Creates birthday events from other calendar's dataGPL-3.0-only

Tuta Calendar

Quantum-safe encrypted planner to schedule & manage your events & sync calendarsGPL-3.0-or-later

Calendar Import-Export

Import, Export & Backup your calendars using ics filesGPL-3.0-only

Hebrew Calendar

Hebrew date, holidays, zmanim and Omer count on your lockscreenMIT

Zanshin Calendar

Tibetan and Japanese calendars with almanac readings, and a meditation timerMPL-2.0

Medical Calendar Log

Privacy-focused medical event tracking using your device's calendar systemGPL-3.0-or-later

Etar - OpenSource Calendar

Etar is a material designed open source calendar, for everyone!GPL-3.0-only

Calendula: Calendar

A Material 3 Expressive calendar for Android with no network access.MIT

Taswast

Amazigh CalendarGPL-3.0-only

Fossify Calendar

Securely plan, schedule, and set reminders with our private calendar app.GPL-3.0-only