WolframAlpha is like a personal interactive encyclopedia. It's the web's premier reference utility covering virtually any subject you can think of: politics, history, math, engineering... It will even tell you how many airplanes are in the sky at any given time on planet Earth.
Make no mistake about it, this is not anything like Wikipedia. WolframAlpha gives a lot dryer information, but it's also factual and not at the mercy of anonymous on-line editors.
For any given input or question, WolframAlpha will provide an array of information and data concerning the subject. Often times this will be accompanied by graphs or pictures.
This app doesn't only deal in historical facts and figures though. It can give you up to date information on employment rates, stock performances, weather conditions and forecasts, and a lot more.
WolframAlpha might very well be the only app you need. For anything. Ever.
Compatible with iPhone, iPod touch, and iPad.