“Wolfram|Alpha‘s long-term goal is to make all systematic knowledge immediately computable and accessible to everyone.” Wolfram|Alpha contains over 10+ trillion pieces of data from primary sources which are constantly being updated along with adding new data sources. They call the product a computational knowledge engine, to distinguish itself from a search engine. Wolfram|Alpha dynamically generates computations depending on your imput.
You can compare crime rates over time in several cities simultaneously, look up ginsing and the result view gives you the CAS number or the taxonomic network in the plant kingdom or compute the odds that two people in a group share a birthday (known in math as the birthday problem). Wolfram|Alpha has a widget builder and just released an API for high performance computing output to your website. Have fun!