**Tutanota** offers a free and encrypted calendar across their supported platforms. Features include: automatic E2EE of all data, sharing features, import/export functionality, multi-factor authentication, and [more](https://tutanota.com/calendar-app-comparison/).
Multiple calendars and extended sharing functionality is limited to paid subscribers.
**Proton Calendar** is an encrypted calendar service available to Proton members via web or mobile clients. Features include: automatic E2EE of all data, sharing features, import/export functionality, and [more](https://proton.me/support/proton-calendar-guide). Those on the free tier get access to 3 calendars, whereas paid subscribers can create up to 25 calendars. Extended sharing functionality is also limited to paid subscribers.
We are working on establishing defined criteria for every section of our site, and this may be subject to change. If you have any questions about our criteria, please [ask on our forum](https://discuss.privacyguides.net/latest) and don't assume we didn't consider something when making our recommendations if it is not listed here. There are many factors considered and discussed when we recommend a project, and documenting every single one is a work-in-progress.
### Minimum Qualifications
- Must sync and store information with E2EE to ensure data is not visible to the service provider.
