Here, an impressive demo of what it promises to be the next big thing on the Internet. Wolfram Alpha is been created by [[Stephen Wolfram]], creator of [[Mathematica]] and it is supposed to become available starting from May 2010. It seems like it could be an amazing example of data mining technology and could prove very useful for bridging technical knowledge to every day curiosities.
And here, a review of a first public demo run.
EDIT [2009/05/17]. Seems the service is online starting from yesterday. You can calculate things like Normality of 37%HCl or your exact age in seconds.