Tuta Calendar
German end-to-end encrypted calendar by Tutao GmbH, tightly integrated with Tuta Mail. All calendar data is encrypted on German servers using post-quantum TutaCrypt encryption. Standalone calendar app launched in 2024. Open source, no ads, no tracking.
Quick facts
Why does it score 100?
Tuta Calendar is built by Tutao GmbH, legally based in Hanover, Germany.
Tutao GmbH is bootstrapped with no outside investors.
Tuta Calendar runs entirely on Tutao's own servers in Germany.
Tuta Calendar is fully open source and uses proprietary post-quantum TutaCrypt encryption. Its servers run on renewable energy.
See how they compare
Tuta CalendarWhat does it replace?
Google Calendar 
Apple Calendar 
Outlook More European Calendar & contacts alternatives
Swiss end-to-end encrypted calendar by Proton AG. All event details (titles, descriptions, locations, attendees) are encrypted so even Proton cannot read them. ISO 27001 certified, independently audited annually by Securitum, own infrastructure in Switzerland and Germany.