Tuta Calendar

Tuta Calendar is the encrypted calendar application from Tutao GmbH, headquartered in Hanover, Germany. Events, attendees, descriptions and notifications are end-to-end encrypted on-device using Tuta's TutaCrypt post-quantum cryptography, so the calendar provider cannot read scheduling data. It supports recurring events, invitations, multiple calendars, reminders and sync across iOS, Android, web and desktop, and is bundled with every Tuta Mail plan, including the free 1 GB tier. The clients are open source.