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ElectroCalc is a free Progressive Web App built for electronics technicians, offering around 50 calculator modules covering areas like power supplies, motor mechanics, household electrical consumption, antenna pointing, and solar PV installation. It also integrates a full technical course, and works offline once installed, making it especially useful in areas with unreliable internet access. It's actively maintained, with modules verified for calculation accuracy before release.
Try it here: https://legend7792.github.io/Electrocalc/