This is the most important tool on the internet. Now.. I'm not saying that WOT makes this tool better than any other COULD... but as far as I'm aware, they're the only one who offers this tool, and they do it very well.
The little circle with the color code system is such a streamlined and efficient way to easily and immediately know if the website you're on is legitimate. It's only downfall is that not enough people use it... with more users comes more reviews and, therefore, the tool works closer and closer to maximum effectiveness.
WOT used to be a very good rating system, but after changing ownership they have been going downhill. "Machine Learning" rates sites safe even when they are fraudulent, dangerous, hateful, or otherwise unsafe, and even when user ratings are poor. Features that used to be free are now behind a paywall, such as checking a website's reputation via the context menu and "parental control" mode.
WOT is a free website reputation, rating and review tool that helps find trustworthy websites and protects against online scams, untrustworthy links, and unreliable web stores. Free add-on for Firefox, IE, Chrome, Opera and Safari browsers.