Blink (Chromium) and WebKit are also closely related as the former is a fork of the later.

So there are effectively only two "independent" engines.

But in reality there is actually none. Both engines exist through Google money.

Given that most people can't even tell the difference between the internet and the web (hello, Arc developers!) and the web became the new all encompassing platform (like MS Windows was before) we have here a very dangerous concentration of power. Almost all private computing is controlled end-to-end by Google these days.

If Microsoft got almost split up for having way less power Google is long long overdue for a divestiture. Should this ever happen (I suspect the US would not give up control of personal computing all over the world so it's imho unlikely, but if) everybody would recognize quite fast how bad the mono-culture in the browser space really is…