If you want to know who your website’s competitors are online—the bigger, more popular ones—this will give you that info.
Enter a site’s URL (a domain should do), and it pumps out a list and profiles of big sites out there with similar content, including a rating percentage of similarity (that’s a nice touch).
Chances are entering your own site won’t work, though. It likes bigger names. Shouldn’t be much of a problem, since you surely must know at least one site out there similar to what you’ve got and reaching the audience you want to reach. Enter that.
Great for market research, by the way, if you’re thinking of creating a niche site. It sure shows you what you’ll be up against.