DomEye was a free online tool that revealed similar websites by analyzing server information from publicly available sources. DomEye detected websites sharing the same Amazon Affiliate Program ID, registered email addresses in the WhoIs, Google Analytics tracking code, Adsense Publisher ID, HiStats ID, IP address and many more. DomEye's database had millions of websites indexed and kept growing every second.
DomEye was free to use, requests where limited to avoid abusive behaviour (you could contact me to lift the limit). If a website was not found DomEye would analyze it in the next few minutes.