WolframAlpha

WolframAlpha is a computational knowledge engine: instead of returning links, it computes an answer from curated data and symbolic mathematics.

It handles what a search engine handles badly — solving equations step by step, unit and currency conversion, statistics on a dataset, plotting a function, or comparing quantities like population and GDP directly.

The free tier answers most queries; step-by-step solutions and extended computation time require a subscription. Its data is curated rather than crawled, so coverage is deep on science, mathematics and reference facts and thin on current events.