calculate.at is a free, ad-supported library of 290+ calculators covering finance, health, math, science, construction, unit conversion, and date/time, plus a small games section. Every tool is single-purpose — unit converters get one page per direction instead of a shared toggle — so results stay matched to the exact question. No account anywhere, and nothing moves behind a paywall later since the whole product runs on ads. Most calculators let you share a result via direct link, and a growing set embed elsewhere as live widgets, with customization or new-calculator requests taken too.
