Comment by lcouturi

Well, they could build their UI using an existing toolkit, like GTK or Qt. Though, when I previously tested Ladybird it seemed to be using GTK and the current AUR package lists Qt as a dependency, so it seems they're already doing that.

They could also rely on existing multimedia libraries for audio/video (ffmpeg). Those are the main things that jump out to me. There's so much ground to cover that there's probably more, though. Maybe SDL for gamepad support?