- Apple has Safari which uses Webkit (which was forked from KHTML as you noted)
- Mozilla has Firefox which uses Gecko (originally from Netscape)
- Google has Chrome which uses Blink (forked from Webkit)
- Microsoft has Edge which uses Blink
- Opera has Opera which uses Blink
... The only two major players currently maintaining a non-Chromium and Blink based browser are Firefox (mentioned by the OP) and Apple (mentioned by myself).
I was simply trying to provide some additional context about the history of Chrome, perhaps I should've also included the context about the history of Safari.
But anyways... blah blah blah
If just rendering engine (but not a browser) then Sciter will qualify I think too. And it is not derived from any others.