I found that the SerenityOS project also has a web browser with a completely new set of engines. It looks reasonably capable too.

Both LibWeb and LibJS are novel engines. I have a personal history with the Qt and WebKit projects, so there’s some inspiration from them throughout, but all the code is new. Not to mention, hundreds of people have worked on the codebase since I started it, all adding their own personal influences, so it’s definitely its own thing.

Edit: Here's a recent interview with the creator Andreas Kling talking to Eric Meyer and Brian Kardell about the browser https://www.igalia.com/chats/ladybird

Edit 2: Here’s their August 2023 update video of the browser https://youtu.be/OEsRW3UFjA0

Edit 3: Looks like the project was recently sponsored $100k USD from Shopify https://awesomekling.substack.com/p/welcoming-shopify-as-a-ladybird-sponsor

It’s quite impressive!

Note: I don't know anything about the politics of the SerenityOS project or the people behind it.