18 open-source calendar and contacts apps
Open Source Calendar & Contacts Apps
The most popular open-source calendar and contacts apps for Android on GitHub are Tuta Calendar, DAVx⁵ and Etar. appsgit lists 18, 17 of them on F-Droid, each with its license, last commit and store links.
Updated Oct 8, 2026
Open Source Calendar & Contacts Apps
Tuta Calendar
tutao/tutanota
Quantum-safe encrypted planner to schedule & manage your events & sync calendars.
OfficialCalendar & contactsAndroidiOS
DAVx⁵
bitfireAT/davx5-ose
CalDAV/CardDAV Synchronization and Client.
Calendar & contactsAndroid
Etar
Etar-Group/Etar-Calendar
Etar is a material designed open source calendar, for everyone!
Calendar & contactsAndroid
Fossify Calendar
FossifyOrg/Calendar
Securely plan, schedule, and set reminders with our private calendar app.
OfficialCalendar & contactsAndroid
Birday
m-i-n-a-r/birday
A simple yet useful birthday manager. Birday is free and ad-free!
Calendar & contactsAndroid
Persian Calendar
persian-calendar/persian-calendar
Android Persian Calendar.
Calendar & contactsAndroid
Fossify Contacts
FossifyOrg/Contacts
Manage your contacts privately and efficiently with vCard support.
OfficialCalendar & contactsAndroid
Connect You
you-apps/ConnectYou
Privacy focused contacts and SMS messenger app build with MD3.
Calendar & contactsAndroidNative
Obiente/native
Adaptive native Nextcloud client for mobile and desktop, with dynamic support for the wider Nextcloud app ecosystem.
Calendar & contactsAndroidiOS
KashCal
KashCal/KashCal
All your calendars in one app. iCloud, CalDAV, device, ICS.
Calendar & contactsAndroid
Casio G-Shock Smart Sync
izivkov/CasioGShockSmartSync
Add smart functions to your Casio square BT G-Shock Watch.
Calendar & contactsAndroidHåck mas Castle 2026 Fahrplan
EventFahrplan/EventFahrplan
Eine Fahrplan-App für Håck ma’s Castle 2026.
Calendar & contactsAndroid
Todo Agenda
andstatus/todoagenda
Home screen widgets displaying events from selected calendars and task lists.
Calendar & contactsAndroid
Birthday Adapter
SufficientlySecure/birthday-calendar
See birthdays and other events from your contacts in your calendar.
Calendar & contactsAndroidFOSDEM Companion
cbeyls/fosdem-companion-android
Schedule browser for the FOSDEM conference.
Calendar & contactsAndroid
Giggity
Wilm0r/giggity
Schedule viewer for conferences and other events.
Calendar & contactsAndroid
MinCal Widget
mvmike/min-cal-widget
Minimal Calendar Widget.
Calendar & contactsAndroid
NovaDial
dhilipmpms/NovaDial
Unlock a secure, open-source calling experience with NovaDialer.
Calendar & contactsAndroid
What are the best open-source calendar and contacts apps?
By GitHub stars, Tuta Calendar is the most popular (7,986 stars), followed by DAVx⁵ and Etar. Each page lists the license, the last commit and the F-Droid, Google Play or App Store link when the project publishes one.
Which of these apps work on iPhone?
2 of the 18 open-source calendar and contacts apps listed here run on iOS, including Tuta Calendar and Native, and 18 run on Android.
Are these apps on F-Droid?
17 of the 18 are on F-Droid, which builds them from source. 15 of those have no anti-features (such as ads, tracking or a non-free network service) flagged by F-Droid; each app page lists any that are.
How are these open-source calendar and contacts apps chosen?
Apps come from the F-Droid index (apps whose source code is on GitHub), GitHub topics such as android-app, flutter-app, ios-app and jetpack-compose, and a short hand-checked list of official apps that are not on F-Droid. An app is listed only if its license is OSI-approved or FSF-free (F-Droid's license first, then GitHub's), the repository has a README and a commit in the last six months and is not archived, and it has 100+ GitHub stars (F-Droid apps) or 300+ stars (everything else). Libraries, SDKs, templates, samples and demo apps are left out. Source-available apps are never listed.