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One Calendar alternatives · Calendar

Open-source alternatives to One Calendar

One Calendar is not described as open source on its own site. 11 of the 75 other calendar and scheduling apps in this directory are open source, according to their own sites.

One Calendar has a free plan. Paid plans start at $5.99 one-time per platform (App Store or Google Play). All of them are free or have a free plan.

11 tools · Listings checked up to Oct 9, 2026 · Where the facts come from

How each one differs from One Calendar

  1. Fossify Calendar

    Open-source Android calendar with no ads, tracking or account

    • Fossify Calendar is free. One Calendar starts at $5.99 one-time per platform (App Store or Google Play).
    • Only One Calendar lists iOS, macOS and Windows apps.
    • Fossify Calendar is open source, according to its own site.
    • One Calendar can be bought with a one-time purchase.
    Fossify Calendar pricing and details

  2. Etar

    Open-source Material Design calendar for Android

    • Etar is free. One Calendar starts at $5.99 one-time per platform (App Store or Google Play).
    • Only One Calendar lists iOS, macOS and Windows apps.
    • Etar is open source, according to its own site.
    • One Calendar can be bought with a one-time purchase.
    Etar pricing and details

  3. GNOME Calendar

    Free, open-source calendar app for the GNOME desktop on Linux

    • GNOME Calendar is free. One Calendar starts at $5.99 one-time per platform (App Store or Google Play).
    • Only GNOME Calendar lists a Linux app.
    • Only One Calendar lists Android, iOS, macOS and Windows apps.
    • GNOME Calendar is open source, according to its own site.
    GNOME Calendar pricing and details

  4. Proton Calendar

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

    • Proton Calendar starts at $3.99 per month, billed every 12 months ($47.88); $4.99 billed monthly. One Calendar starts at $5.99 one-time per platform (App Store or Google Play).
    • Only Proton Calendar lists a web app.
    • Only Proton Calendar lists a Linux app.
    • Proton Calendar is open source and end-to-end encrypted, according to its own site.
    Proton Calendar pricing and details

  5. Tuta Calendar

    End-to-end encrypted calendar bundled with Tuta Mail

    • Tuta Calendar starts at €3 per month, paid yearly (€3.60 paid monthly). One Calendar starts at $5.99 one-time per platform (App Store or Google Play).
    • Only Tuta Calendar lists a web app.
    • Only Tuta Calendar lists a Linux app.
    • Tuta Calendar is open source and end-to-end encrypted, according to its own site.
    Tuta Calendar pricing and details

  6. Itsycal

    Free, tiny menu bar calendar for the Mac

    • Itsycal is free. One Calendar starts at $5.99 one-time per platform (App Store or Google Play).
    • Only One Calendar lists Android, iOS and Windows apps.
    • Itsycal is open source, according to its own site.
    • One Calendar can be bought with a one-time purchase.
    Itsycal pricing and details

  7. MeetingBar

    Free Mac menu bar app that shows and joins your next meeting

    • MeetingBar is free. One Calendar starts at $5.99 one-time per platform (App Store or Google Play).
    • Only One Calendar lists Android, iOS and Windows apps.
    • MeetingBar is open source, according to its own site.
    • One Calendar can be bought with a one-time purchase.
    MeetingBar pricing and details

  8. Merkuro Calendar

    Open-source calendar and task app from KDE for Linux

    • Merkuro Calendar is free. One Calendar starts at $5.99 one-time per platform (App Store or Google Play).
    • Only Merkuro Calendar lists a Linux app.
    • Only One Calendar lists Android, iOS, macOS and Windows apps.
    • Merkuro Calendar is open source, according to its own site.
    Merkuro Calendar pricing and details

  9. Timeful

    Free, open-source group availability poll with calendar autofill

    • Timeful is free. One Calendar starts at $5.99 one-time per platform (App Store or Google Play).
    • Only Timeful lists a web app.
    • Only One Calendar lists Android, iOS, macOS and Windows apps.
    • Timeful is open source and self-hostable, according to its own site.
    Timeful pricing and details

  10. Rallly

    Open-source meeting polls for finding a time that suits a group

    • Rallly starts at $6 per seat / month, billed yearly ($10 billed monthly). One Calendar starts at $5.99 one-time per platform (App Store or Google Play).
    • Only Rallly lists a web app.
    • Only One Calendar lists Android, iOS, macOS and Windows apps.
    • Rallly is open source and self-hostable, according to its own site.
    Rallly pricing and details

  11. Crab Fit

    Free, open-source availability heat map for group events

    • Crab Fit is free. One Calendar starts at $5.99 one-time per platform (App Store or Google Play).
    • Only Crab Fit lists a web app.
    • Only Crab Fit lists a browser extension.
    • Only One Calendar lists iOS, macOS and Windows apps.
    Crab Fit pricing and details

Common questions

Is there an open-source alternative to One Calendar?

Yes. Fossify Calendar, Etar, GNOME Calendar, Proton Calendar, Tuta Calendar, Itsycal, MeetingBar, Merkuro Calendar and 3 more are open source, according to their own sites.

Is One Calendar open source?

One Calendar is not described as open source on its own site. The listing was checked on Oct 9, 2026 against the pages it cites.

When was this checked?

Each listing shows its own date. On this page they run from Oct 5, 2026 to Oct 9, 2026. Vendors change prices and plans without notice, so confirm on their site before you buy.

This page is built from the listings. A tool is here because its listing says so, and the order is how close each is to One Calendar: the alternatives its listing names first, then the tools that share the most features with it.