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DumberKit: Calculator

Calculator, unit and currency converter for keypad phones
New in version 1.1.0
• New currency converter with the European Central Bank's rates, works offline with the last ones
• No more "fake version" warnings
• The selected dialog button is easier to see
A calculator, unit converter and currency converter for keypad phones like the Qin F21, Dumber Mini or Doov R77 Pro. There are no on-screen buttons: you type the calculation straight on the keypad and press OK for the result. Touch is switched off inside the app, so nothing gets pressed by accident in your pocket.

Keys
• 0–9 – type numbers
• * – add an operator, press it again for the next one (+ − × ÷)
• Hold * – a palette of symbols laid out like the keypad: ^, √, parentheses, %, ±
• # – decimal point
• OK or Call – show the result
• Back – delete the last character; hold it to clear everything
• ↑ / ↓ – go through the history
• ← / → – switch between Calculator, Unit converter, Currency converter and Settings

Features
• The usual order of operations and exact decimals (0.1 + 0.2 = 0.3)
• History like a paper tape, cleared when you close the app
• Unit converter for length, area, volume, mass, temperature, time, speed, pressure and energy, in both directions
• Currency converter with about 30 currencies at the European Central Bank's rates, works offline with the last ones
• Copy the result, or take a converted value over to the calculator
• System, light, dark, dark red and custom themes, a keypad-friendly color picker, blue or any other icon color
• No ads, no tracking; internet only for the ECB's currency rates

Based on Fossify Calculator (GPL-3.0), keypad input inspired by Calc-U-Later.
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Versions

Although APK downloads are available below to give you the choice, you should be aware that by installing that way you will not receive update notifications and it's a less secure way to download. We recommend that you install the F-Droid client and use that.

Download F-Droid
  • Version 1.1.0 (3) suggested Added on Oct 22, 2026

    arm64-v8a armeabi-v7a x86 x86_64

    This version requires Android 8.0 or newer.

    It is built and signed by the original developer, and guaranteed to correspond to this source tarball.

    Permissions
    • have full network access
      Allows the app to create network sockets and use custom network protocols. The browser and other applications provide means to send data to the internet, so this permission is not required to send data to the internet.
    • org.fossify.android.permission.WRITE_GLOBAL_SETTINGS

    Download APK 3 MiB PGP Signature | Build Log

    • New in version 1.0.0
    First release: calculations typed straight on the keypad with the usual order of operations, a symbol palette on a held *, a history you can go through with up / down, and the unit converter and settings in tabs switched with left / right.
  • Version 1.0.0 (2) - Added on Oct 14, 2026

    arm64-v8a armeabi-v7a x86 x86_64

    This version requires Android 8.0 or newer.

    It is built and signed by the original developer, and guaranteed to correspond to this source tarball.

    Permissions
    • org.fossify.android.permission.WRITE_GLOBAL_SETTINGS

    Download APK 3 MiB PGP Signature | Build Log

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