It is the computational knowledge engine, released in the Summer of 2009 by Wolfram Research, makers of Mathematica and maintainers of the MathWorld reference library. I followed the project loosely from buzz to release. It was rumored to be a Google rival, also having strong mathematical underpinnings. While it may take some traffic from Google, Wolfram|Alpha was not designed to be a direct competitor - it is not concerned with searching the web.
Wolfram|Alpha is made up of very high-end supercomputing clusters, running various derivatives of their Mathematica software for the web and for supercomputing, and a mind-boggling number of statistical and other reference material that is structured in such a way that the software can compute a result for your query.
The data that they use is peer-reviewed and accurate, and beyond retrieving statistics and displaying trends (such as rainfall patterns or economic prosperity for a given region), Wolfram|Alpha can actually compute your query, if it concerns mathematics, science, or engineering. Check out the example queries to get a feel for what it can do in each subject area.
Read about it and start computing! Think twice next time you need some numbers for a report - try Wolfram|Alpha first - you may be pleasantly surprised!
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