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Proton Calendar vs calcurse: catalog facts
Proton Calendar	calcurse
Freemium Free account available, with paid Proton plans and a business version.	Free Free to download, with donations accepted.
Android, iOS, Web	Linux, Command line
End-to-end encryption of event details Built-in scheduling for booking meetings	Recurring appointments, all-day events and to-dos Scriptable command-line mode
Requires a Proton account Works best within the Proton ecosystem	CalDAV sync is experimental Terminal interface only
Downloadable app, Web application, Hosted service	Downloadable app
Closed source	Open source
License not stated	License not stated
Account needed	No account needed
Not stated if it works offline	Works offline
Official website Full listing and sources Checked September 23, 2026	Official website Full listing and sources Checked September 24, 2026

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