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Standalone, open-source encrypted calendar with quantum-safe end-to-end encryption and a zero-knowledge architecture that hides even your event metadata from the server.
Tuta Calendar is a free, open-source calendar app built with the same end-to-end encryption standards as Tuta Mail, encrypting entire events by default — including titles, notifications, and reminders so that nothing about a user's schedule is ever visible to Tuta's servers. It uses a zero-knowledge architecture with quantum-safe encryption, meaning even metadata like meeting times or attendees stays hidden from the provider. Users can send and receive calendar invitations via the standard .ics format, including to people who don't use Tuta, with optional password protection for external invites. The app supports multiple calendars, calendar sharing between Tuta users, daily/weekly/monthly views that work offline, and push notifications delivered securely so no third party can track event activity. Tuta Calendar is available as a standalone app for Android (including F-Droid), iOS, Linux, Windows, and macOS, or through the browser, and integrates seamlessly with Tuta Mail so both tools can be used from a single account. Tuta is based in Germany, fully GDPR-compliant, hosted in ISO 27001-certified data centers, and powered entirely by renewable energy. The client code is open source, sharing its codebase with the wider Tuta project on GitHub.
