fruux is a calendar service from Germany. Their CalDAV server is open source.
European calendar services
A calendar service is a digital calendar that helps users manage appointments and scheduling. Calendar services often offer shared calendars where different people can see and create events. In order to sync entries to different devices, most calendar services offer an iCalendar interface. iCalendar is an open standard for the exchange of calendar content.
This category contains services from companies based in a member state of the European Union (EU), the European Economic Area (EEA) and the European Free Trade Association (EFTA).
You can read more about the listing criteria here.
Proton Calendar is a calendar service with a strong focus on privacy based in Switzerland. Proton Calendar uses zero-knowledge encryption, which means that the company can not read the content of your calendar even if they are stored on their servers.
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