I really think this is going the change the internet the way google has. Basically, instead of returning search results, it returns search answers. So, rather than returning a list of relevant webpages, it runs computations on them in the background to give you the answer that you're looking for. It's the project of Stephen Wolfram (the brains behind Mathematica).
It's sort of hard to explain, so here are a few examples:
Want to know the nutritional values of 2 pieces of swiss cheese? 2 slices of swiss cheese - Wolfram|Alpha
What about the detriot lions rushing yards per game? Detroit Lions rushing yards per game - Wolfram|Alpha
Comparison on passing touchdowns in history of the Cowboys and the Broncos... passing touchdowns Dallas Cowboys, Denver Broncos - Wolfram|Alpha
Want to know the stopping distance of a car going 70MPH? stopping distance 70mph - Wolfram|Alpha
Thinking about being an intercity bus driver and want to know the salary? intercity bus driver salary - Wolfram|Alpha
Who wrote stairway to heaven? Who wrote Stairway to Heaven? - Wolfram|Alpha
Of course it does awesome math stuff with Mathematica engine running in the background: http://www85.wolframalpha.com/input/?i=factor+2x^5+-+19x^4+%2B+58x^3+-+67x^2+%2B+56x+-+48
I think you get the idea. It was literally just released, so I'm sure it will change alot as time goes on... but it's already awesome.