Apple’s WebKit (WebCore+JavaScriptCore) was originally a fork of KHTML/KJS. They shared at the beginning but not very well. They eventually opened up their source and made changes that were more friendly to other developers. A lot of browsers and embedded renderers use WebKit, now, besides Safari and KDE based ones.

Google forked WebCore for Chromium. I don’t think they share a codebase, anymore. Edge, Opera and many embedded renderers use Chromium.

Anyway, I just think it’s interesting that most every browser out there is descended from KHTML.