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Etar vs Proton Calendar: catalog facts
Etar	Proton Calendar
Free Free and open source.	Freemium Free account available, with paid Proton plans and a business version.
Android	Android, iOS, Web
Open source with an active community Clean Material Design interface	End-to-end encryption of event details Built-in scheduling for booking meetings
Android only Sync depends on the calendar accounts set up on the phone	Requires a Proton account Works best within the Proton ecosystem
Downloadable app	Downloadable app, Web application, Hosted service
Open source	Closed source
License: GPL-3.0	License not stated
Not stated if an account is needed	Account needed
Not stated if it 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.