Sums is a postfix calculator designed for quick calculations and focused on simplicity.
It adheres to GNOME’s human-interface guidelines. It is designed to be keyboard-driven and aims to feel natural to interact with by recognising English-language input as mathematical constants and operations.
For example, the expression 1 2 pi 4 5 sum will return the result 15.1415926. Expressions will also be converted as you type to display mathematical symbols where possible. The previous example would be displayed as 1 2 π 4 5 Σ.
This is free and open source software.
Key Features
- A selection of core mathematical operations and constants.
- Two-way history navigation.
- Copying your results with one click.
Website: gitlab.com/leesonwai/sums
Support:
Developer: Joshua Lee
License: GNU General Public License v3.0

Sums is written in C. Learn C with our recommended free books and free tutorials.
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My favorite calculator for a long time now is SpeedCunch.
Yes great software along with Qalculate!