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Proton Calendar vs Nextcloud Calendar: catalog facts
Proton Calendar	Nextcloud Calendar
Freemium Free account available, with paid Proton plans and a business version.	Free Free app for Nextcloud servers.
Android, iOS, Web	Web, Self-hosted
End-to-end encryption of event details Built-in scheduling for booking meetings	Calendars stay on your own server CalDAV sync with standard clients
Requires a Proton account Works best within the Proton ecosystem	Requires a running Nextcloud server Not a standalone app
Downloadable app, Web application, Hosted service	Self-hosted
Closed source	Open source
License not stated	License not stated
Account needed	Account needed
Not stated if it works offline	Not stated if it works offline
Official website Full listing and sources Checked September 23, 2026	Official website Full listing and sources Checked October 2, 2026

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