GenCircles - http://www.gencircles.com - (now absorbed into MyHeritage) - was a site where individuals could enter their relatives' details and find links to others.
The focus of this site has been said to be on family lineages. One of its features was "smartmatching", giving you a list of other genealogies on the site where an apparent match was found.
This page is a "stub" and could be improved by additions and other edits.