Wolfram Alpha

Wolfram Alpha is a computational knowledge engine.

This has an incalculable amount of uses.
Wolfram Alpha aims to collect and curate all objective data.
Go to their about page to learn more.

This to me, is extremely important.

How it relates to design–

Since Wolfram Alpha is so broad, I'll talk about how it relates to design.

Research.
Any objective research needed about any client will likely be listed in Wolfram Alpha.
If your client had a website, you can search their URL in Wolfram's search engine and it will give you all objective data about the site.

For example; I searched www.blogger.com and this is the information that was collected.
http://www.wolframalpha.com/input/?i=www.blogger.com

daily page views | ~~ 250 million 
daily visitors | ~~ 31 million 
site rank | ~~ 40th
domain online | 22-06-1999  (~~13 years ago)
(based on Alexa estimates, as of  07-03-2012)

page title | Blogger: Create your free blog
page size | 12.05 kB  (excluding images, stylesheets, etc.)
links from page | 30  (in HTML)
images on page | 1
forms on page | 2  (8 input fields)

company name | Google, Inc.
location | Mountain View, California, United States
market cap | $196.7 billion
employees | 32467 people