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

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