It's a simple tool and can often come in handy but not many SEO tool sites have it.
You type a keyword in the form and the tool will return the list of domain and URLs in a table format exactly in the same order as Google SERPs. The tool will return 100 search results.
Type a certain keyword and google it, get the domains highly ranked for that keyword and start studying the PR and Domain Authority etc. If you are living off of SEO work, the chances are that you have done that. This tool might speed up that tedious work a little bit.