What am I missing here? Web browsers are already GUIs, and any backend with an api supports it.
Reading the “How Does it Work?” section of the readme, I interpret it as WebUI being a way of embedding a web view into your existing program, being a sort of proxy for the existing browser of the system. https://github.com/webui-dev/webui#how-does-it-work
I couldn't tell from their docs what makes their project unique compared to these existing and more popular solutions.