Want to know a diffraction pattern for a circular aperture? Need to compare several different ions? Or just can't remember who sang "Stairway to Heaven"? Try Wolfram|Alpha, a computational knowledge engine that generates output by doing computations from its own internal knowledge base instead of searching the web and returning links.
Wolfram|Alpha is not a search engine, but can certainly help with comparisons, computations, and those little trivia questions that you come across on a daily basis. Since it isn't a search engine, it does have certain limitations: it can only know things that are known, and are somehow public. It only deals with facts, not opinions. It limits the computation time for each query. And, of course, it's in continual development. However, that also means that new knowledge will continue to be added to its knowledge base, making it more valuable and helpful as it grows. Check out some of the examples to see what it can do.