Impressive work!

And oddly, it would be even more impressive if they built their own Web Browser from scratch ...

https://github.com/SerenityOS/serenity/tree/master/Ladybird

I also like their Jakt programming language:

https://github.com/SerenityOS/jakt

Though I'm more enthusiastic about Redox (doing it in Rust):

https://gitlab.redox-os.org/redox-os/redox/