fend
Calculate with arbitrary precision and convert between physical units.
fend is a unit-aware calculator available as a command-line application and a browser interface. It supports rational-number arithmetic, complex numbers, variables, trigonometry, number-base conversion, and dice-roll expressions.
Its calculation engine and CLI are implemented in Rust. A WebAssembly wrapper exposes the same core to the web interface. Unit support includes SI, US and UK customary units, and historical measures.