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Proton CalendarEtar
Freemium

Free account available, with paid Proton plans and a business version.

 Free

Free and open source.

Android, iOS, Web Android
  • End-to-end encryption of event details
  • Built-in scheduling for booking meetings
  • Open source with an active community
  • Clean Material Design interface
  • Requires a Proton account
  • Works best within the Proton ecosystem
  • Android only
  • Sync depends on the calendar accounts set up on the phone
Downloadable app, Web application, Hosted service Downloadable app
Closed source Open source
License not stated License: GPL-3.0
Account needed Not stated if an account is needed
Not stated if it works offline Not stated if it works offline

Checked September 23, 2026

Checked September 24, 2026

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