Web search engines like Google support boolean search commands (AND, NOT, OR) to help you narrow down or widen results.
For instance, mp3 player -iPod will search for mp3 players other than iPod while a query like grand auto theft +review on Google News will show news stories that contain reviews of this popular video game.
Using boolean operators may be second nature to most web veterans but if you ever need to explain the same concept to a newbie or your kids, Boolify can be a big help.
Boolify is visual query builder that works with Google web search, Images and News search. You begin by dragging blocks on the canvas - these blocks, that resemble jigsaw puzzle pieces, actually represent the boolean operators.
The search results from Google will appear and change instantly as you add (or remove) boolean operators from the search query. Give it a shot.