Google X is the name of two products.
One was a project first started on March 15, 2005 from Google Labs. The next day it disappeared. It had the normal Google Search bar, along with some other buttons designed to look like Apple's Mac OS X.
The other is a top-secret lab (Speculations say it is found in the bay area of Northern California) where Google invents what was previously thought impossible. There are currently 100 ideas that they are working on, they expect some of the more realistic ones to be done as soon as the end of 2012. Here is a list of known projects: