Ladybird is an ongoing project to build an independent web browser from scratch.
It is being developed as part of the SerenityOS/serenity project on GitHub.
There are no downloadable binaries yet, as the project is still very unstable. You can follow the build instructions to build it for yourself.
This page is not fancy because we are focusing on building the browser. :^)
Since Ladybird is part of the SerenityOS project, development is coordinated on the SerenityOS discord server.
We essentially have three different browsers, that definitively isn't "lots and lots". Every year they get together and agree on what measures can be foisted upon all users with or without their support. The rest are very little more than reskins of each other.
Ok, so what do you want your 4th, new browser to do differently? What's so different about it that you can't build it on top of Gecko?
It's not about a lack of features.
What is it about then? Rendering HTML and CSS in a new, fun way?
No? I've already said what it's about, and I'm not eager to repeat myself 'cause I feel vague meanyness.
What you said (if I understand you correctly, you didn't give any examples) boils down to breaking standards established by the current browsers. The standards that web developers and servers universally follow. If you want to build browser that will not follow standards you might just as well render HTML in non-standars ways. Most pages will not work anyway.