Wolfram Alpha

http://www.wolframalpha.com/

Wolfram Alpha is an answer engine developed by Wolfram Research ( Wolfram Research is an international company that summarizes its aim as "Pushing the Envelope of Technical Computing". The main product of Wolfram Research is Mathematica, an environment for technical computing. ) and it was released to the public on May 15, 2009.

As of now, WolframAlpha contains 10+ trillion pieces of data, 50,000+ types of algorithms and models, and linguistic capabilities for 1000+ domains. Built with Mathematica—which is itself the result of more than 20 years of development at Wolfram Research—WolframAlpha's core code base now exceeds 5 million lines of symbolic Mathematica code. Running on supercomputer-class compute clusters, WolframAlpha makes extensive use of the latest generation of web and parallel computing technologies, including webMathematica and gridMathematica.

Is WolframAlpha a search engine?

No. It's a computational knowledge engine: it generates output by doing computations from its own internal knowledge base, instead of searching the web and returning links.
The major difference between other seach engine and wolframalpha is others givings the results of site links which included the content but wolframalpha answering your question

Please check bellow examples
the keyword whcih i am searching : doha to newyork
Result link : http://www06.wolframalpha.com/input/?i=doha+to+newyork

It displaying the distance between ny and doha ,flight time , path image view in world map, local times of both city and many more

Another example
if you search some musical notes : C E G Bb D F# A Search link with key word : http://www09.wolframalpha.com/input/?i=C+E+G+Bb+D+F%23+A
It displaying musical notes and can hear the sound ( music ) , keyboard display etc

Click on link to see example by topics : http://www.wolframalpha.com/examples/