http://www.wolframalpha.com/
Esiste anche l'app per iphone e ipad che fa egregiamente il suo dovere. Costa € 1,59 ma li vale tutti.
La localizzazione è solo in inglese, per cui le domande vanno poste in inglese.
Founded by Stephen Wolfram in 1987, Wolfram Research is one of the world's most respected software companies—as well as a powerhouse of scientific and technical innovation. As pioneers in computational science and the computational paradigm, we have pursued a long-term vision to develop the science, technology, and tools to make computation an ever-more-potent force in today's and tomorrow's world.