Proton Calendar
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.
Quick facts
Why does it score 95?
Proton Calendar is incorporated in Geneva, Switzerland, an EFTA country rather than a full EU member state.
The non-profit Proton Foundation holds a controlling stake in Proton.
Proton Calendar runs on Proton's own infrastructure across Switzerland, Germany and Norway.
Proton Calendar is fully open source and independently audited every year by Securitum.
See how they compare
Proton CalendarWhat does it replace?
Google Calendar 
Apple Calendar 
Outlook More European Calendar & contacts alternatives
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.