It's not a "recreation of Windows XP that runs in the browser" but more like "JavaScript application that looks like Windows XP", before anyone becomes disappointed. Sadly, it doesn't even get the iconic three icons right in the application bars ( https://i.imgur.com/agDlohB.png )
Hah, just like LLM gives you a simulation of something understanding and being intelligent, this is something that appears to be an operating system, but is just the parts you interact with and not much underneath.