Wolfram Alpha / a computational knowledge engine

Wolfram Alpha generates output by doing computations from its own internal knowledge base, instead of searching the web and returning links. It make all systematic knowledge immediately computable and accessible to everyone. So it aims to collect and curate all objective data; implement every known model, method, and algorithm; and make it possible to compute whatever can be computed about anything. Please check it out, play around and learn so many cool things! It is also available for you iPhone or iPod Touch. 

Graphical overview of an example