Etar vs Proton Calendar

Price, platforms and features side by side. The table says where each price was read and when.

Etar

Open-source Material Design calendar for Android

Free

Proton Calendar

End-to-end encrypted calendar from the maker of Proton Mail

Free plan · from $3.99/mo

Where they differ

Etar is free. Proton Calendar starts at $3.99 per month, billed every 12 months ($47.88); $4.99 billed monthly.
Only Proton Calendar lists a web app.
Only Proton Calendar lists macOS, Windows, Linux and iOS apps.
Proton Calendar is end-to-end encrypted, according to its own site.
Proton Calendar also covers booking links.

In commonFree planAndroidOpen sourceCalendar

	Etar	Proton Calendar
Pricing	Free	Free plan
Starts at	Free	$3.99 per month, billed every 12 months ($47.88); $4.99 billed monthly
Free plan	Free and open source under the GPLv3. The app is installed from F-Droid or built from the source on GitHub, and the project lists no paid version.	Proton Free: 3 personal calendars with end-to-end encryption and event invitations. No calendar sharing or booking pages, and the desktop app is a 14-day trial.
Free trial	None listed	None listed
Web
macOS
Windows
Linux
iOS
Android
Made by	The Etar Project	Proton AG
Price read from	github.com	proton.me
Checked	Oct 9, 2026	Oct 5, 2026

Etar

Proton Calendar

Etar

Android only; the F-Droid build of version 1.0.57 requires Android 6.0 or newer.
No CalDAV client is included. Syncing a calendar with a server needs another app, such as DAVx5.
The project describes its ICS import as unstable and advises caution if your provider sends invitation emails automatically.
The Google Play link in the project's README returned a Not Found page on the check date; F-Droid carries the current version.

Proton Calendar

Proton Free allows 3 personal calendars; Mail Plus and higher plans allow 25.
Calendar sharing and booking pages need a paid plan, and Mail Plus and Proton Unlimited include only 1 booking page.
Calendar has no subscription of its own: paid features come with Mail Plus, Proton Unlimited or a business plan.
Desktop use is through the Proton Mail app for Mac, Windows and Linux, a 14-day trial on free accounts; the Linux app is labeled beta.

Etar

Month, week, day and agenda views: Four views in a Material Design interface with dark and light themes. Recent versions let the week start on any day and can stagger overlapping events.
Works with any Android calendar provider: Etar reads Android's calendar storage, so it shows every calendar synced to the phone. You choose which ones are displayed and which one new events go to.
Offline calendars: A calendar can be created that is stored on the phone only and never synced to a server.
ICS sharing, import and export: Calendars can be shared as ICS files and imported or exported from storage, including invitations received by email. The project warns that import has known bugs.
Agenda widget: A home screen widget lists upcoming events in agenda form. The interface is translated into many languages by volunteers.

Proton Calendar

End-to-end encrypted events: An event's title, description, location and attendees are encrypted on your device. Events received from people on other calendar services are stored with zero-knowledge encryption.
Appointment booking pages: Publish a booking page that shows only the times you choose and syncs with your calendars to prevent double bookings. Confirmed meetings can include a Proton Meet link. Paid plans only.
Calendar sharing: On paid plans, share a calendar by link or by inviting people directly, showing either full event details or only your availability.
Works with Proton Mail: Send invitations from a Proton Mail address, manage them without leaving the inbox, and add events received by email, such as flights or meetings, to the calendar.
Recurring events and reminders: Events can repeat daily, weekly, monthly or on a custom pattern, with several reminders or email alerts each. Views switch between day, week and month.
Import and calendar subscriptions: The Easy Switch tool imports existing calendars from other providers, and you can subscribe to calendars that other people keep on a different service.

Etar

Etar$0
The complete app, built and signed by F-Droid from the public source code. Version 1.0.57 requires Android 6.0 or newer.

Proton Calendar

Proton Free$0
3 personal calendars, end-to-end encryption, and sending and receiving invitations.
Mail Plus$3.99
per month, billed every 12 months ($47.88); $4.99 billed monthly
25 personal calendars, calendar sharing and 1 booking page, plus 15 GB of storage and 10 email addresses.
Proton Unlimited$9.99
per month, billed every 12 months ($119.88); $12.99 billed monthly
The same calendar features as Mail Plus, bundled with 500 GB of storage and Proton's VPN, password manager and cloud storage.
Workspace Standard$12.99
per user / month, billed every 12 months ($155.88)
Business suite with 25 calendars and 25 booking pages per user, 1 TB of storage per user and 15 custom email domains.
Workspace Premium$19.99
per user / month, billed every 12 months ($239.88)
Everything in Workspace Standard, plus 3 TB of storage per user, 20 custom email domains and data retention policies.
EnterpriseCustom
All Proton services in a customizable package with a dedicated account manager; priced through sales.

Etar

No public discounts listed.

Proton Calendar

Annual discount
20% off Mail Plus on the 12-month plan
Proton's pricing page lists Mail Plus at $3.99 a month when billed every 12 months ($47.88), against $4.99 billed monthly. Proton Unlimited is $9.99 instead of $12.99.
Education
Student discount for the first 12 months
Students verified through Student Beans get 50% off Mail Plus and 62% off Proton Unlimited for the first 12 months; the plan then renews at the regular price.
Nonprofit
Reduced pricing for registered nonprofits
Registered nonprofits can request discounted pricing on Proton's business plans from the sales team. No fixed percentage is published.