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OneCalendar vs Rainlendar: catalog facts
OneCalendar	Rainlendar
Free Free to download from the app stores.	Freemium Lite is free; a Pro licence costs 9.95 EUR.
Windows, macOS, Android, iOS	Windows, macOS, Linux
Supports Google, Outlook, Exchange, iCloud, CalDAV and many other providers Available on Android, iPhone, iPad, Mac and Windows	Calendar and tasks always visible on the desktop Skinnable, with a skin tutorial and API reference
Closed source No Linux version	Some features need the paid Pro edition Closed source
Downloadable app	Downloadable app
Closed source	Closed source
License not stated	License not stated
Not stated if an account is needed	No account needed
Works offline	Not stated if it 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.