most defunct / unmaintained and the three: blink, gecko and webkit being the only ones actively developed and maintained today (I am aware of Goanna, but some articles online say it isn’t being developed anymore – I could be wrong).
The fourth most developed browser engine is Ladybird, spun off from the SerenityOS project. It’s very active. And then you have Mozilla’s Servo… kinda. And then Goanna is still maintained, but not too active.
I’m fairly excited about Ladybird because it’s already gotten 423 on html5test vs Firefox 128’s 544. I do agree that they’re currently pretty much alpha quality, though.