Screenshot with the Tuta Calendar on How to Geek's website: Keep Your Calendar Private Your calendar dailies and agendas are sensitive data that you might want to keep private. You can quickly replace Google Calendar with Tuta Calendar. It's open source and cross-platform, so it syncs across devices. Install it from F-Droid and sign up for a free Tuta mail account. Once that's done, you can import your schedule and agenda into the Tuta calendar. First, export the schedule from your current app in a .ics format and tap the three dots in the Tuta Calendar sidebar. Choose import and select the .ics file, and the app will instantly update with your dailies.