Wolfram Research is working on a "computational knowledge engine" that will return answers in natural-language. The Wolfram|Alpha service is designed to directly compute answers about a wealth of topics based on natural-language questions. For instance, you'll be able to ask Wolfram what the average rainfall in your city was last year, and instead of giving you a list of links like search engines like Google do, the service will deliver a real answer to your question.
It doesn't simply return documents that (might) contain the answers, like Google does, and it isn't just a giant database of knowledge, like the Wikipedia. It doesn't simply parse natural language and then use that to retrieve documents, like Powerset, for example.
Instead, Wolfram Alpha actually computes the answers to a wide range of questions -- like questions that have factual answers such as "What is the location of Timbuktu?" or "How many protons are in a hydrogen atom?," "What was the average rainfall in Boston last year?," "What is the 307th digit of Pi?," "where is the ISS?" or "When was GOOG worth more than $300?"
Think about that for a minute. It computes the answers. Wolfram Alpha doesn't simply contain huge amounts of manually entered pairs of questions and answers, nor does it search for answers in a database of facts. Instead, it understands and then computes answers to certain kinds of questions.