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Fossify Calendar vs OneCalendar: catalog facts
Fossify Calendar	OneCalendar
Free Free and open source with no ads.	Free Free to download from the app stores.
Android	Windows, macOS, Android, iOS
No ads or tracking Syncs with Google, Outlook, Nextcloud and Exchange calendars	Supports Google, Outlook, Exchange, iCloud, CalDAV and many other providers Available on Android, iPhone, iPad, Mac and Windows
Android only Sync relies on accounts already set up on the device	Closed source No Linux version
Downloadable app	Downloadable app
Open source	Closed source
License: GPL-3.0-only	License not stated
No account needed	Not stated if an account is needed
Works offline	Works offline
Official website Full listing and sources Checked October 2, 2026	Official website Full listing and sources Checked October 2, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.