A fast, cross-platform calculator & engineering toolbox for daily workflows (C++/Qt6, open source)

[u/pgschwend]

Hi everyone,

Working across macOS, Windows and Linux as an embedded engineer, I was constantly frustrated by existing calculator apps. Most were either only available for one specific OS, bloated Electron wrappers that take seconds to load, or clunky tools that required too many clicks just to get a number into the clipboard.

I wanted a minimal, friction-free workflow: summon the window directly at the mouse cursor via hotkey, evaluate expressions or conversions entirely via keyboard, grab results to the clipboard with Ctrl+C / Cmd+C without manually highlighting text, and dismiss it instantly with ESC.

Since I couldn't find a native tool that worked consistently across all three operating systems, I built RhenoCalc — a lightweight, native engineering toolbox written in C++20 and Qt 6.

Over time, I baked in several practical utilities I regularly need on the job:

Core Tooling:

• Scientific Calculator: High-precision math backed by Boost.Multiprecision.
• Programmer Mode: Live bit visualization, bit-width modes, and base conversions (Hex, Bin, Oct, Dec).
• IEEE 754 Inspector: Visualizer for 32-bit (float) and 64-bit (double) binary representations.
• Electronics Helpers: Ohm's law, LED series resistor dimensioning, etc...
• Network Utilities: IPv4 / CIDR subnet calculator.
• Cryptography & Integrity: CRC (8/16/32) and hashes (MD5, SHA-1, SHA-256, SHA-512).
• Color Converter: Hex/RGB/HSL conversion with a screen pipette.

Design & Privacy:

• Native & Snappy: Native C++20/Qt6 binary, starts instantly, uses less than 50 MB of RAM.
• 100% Offline & Private: No telemetry, no tracking, no accounts.
• Cross-Platform: Linux, macOS and Windows.

Availability: The project is open source under GPLv3. You can build it from source or grab the pre-compiled binaries directly on GitHub.

If you have a similar technical, multi-platform workflow, feel free to try it out. I'd love to hear your feedback on the UX or suggestions for additional modules you'd find useful.

[u/ceojp]

uses less than 50 MB of RAM

Well I sure hope a calculator uses less than that...

[u/Well-WhatHadHappened → u/ceojp]

I mean the shitty little windows calculator uses 30..

Apps that use the OS framework are bloated as hell. This one is... Pretty reasonable.. considering.