WolframAlpha is a free and open computational knowledge engine that retrieves factual information on just about anything you can think of. Enter a math formula, and get the solution as well as a proof. Input a unit of measurement, and get all conversion possiblities. Ask about a city, and learn the population, unemployment rate, cost of living, etc. It covers everything from mathematics, physics, dates and times, sports, units of measure, history, linquistics – if you can think of it, you can probably find it. According to its FAQ, it contains trillions of pieces of data and growing!

WolframAlpha pulls its information from external sources, as well as an internal knowledge base of data derived from official public and private websites and other primary sources, compiled and organized by WolframAlpha folks. A “Source information” button at the bottom of results pages provides sources and references to data retrieved. Check the site FAQ for more information about the site and its content. Click the link above to begin filling your knowledge base!