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KashCalProton Calendar
Free

Free and open source with no ads.

 Freemium

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

Android Android, iOS, Web
  • iCloud calendar sync on Android
  • Works with Nextcloud, Fastmail and other CalDAV servers
  • End-to-end encryption of event details
  • Built-in scheduling for booking meetings
  • Android only
  • Calendar only, no task or contact management in the app
  • Requires a Proton account
  • Works best within the Proton ecosystem
Downloadable app Downloadable app, Web application, Hosted service
Open source Closed source
License: Apache-2.0 License not stated
No account needed Account needed
Not stated if it works offline Not stated if it works offline

Checked October 2, 2026

Checked September 23, 2026

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