ConvertAll

ConvertAll is an open-source unit converter where, instead of choosing from a fixed list of categories, you type any combination of units, such as kilonewtons per square metre or litres per second, and it checks the dimensions and converts. Any unit can take an SI prefix, units can be searched and filtered as you type, fractions are converted and results can be shown in engineering notation. It was rewritten in Flutter and runs on Windows, Linux, Android and in the browser. It suits quick checks of pressure, flow, energy and load conversions between SI and imperial units. Limitation: there is no macOS version, and it converts units only rather than being a full calculator.