Yeah, the GitHub link is totally dead. Honestly, the site looks kinda sketchy, like a Coinb.in clone but with some tweaks. I wouldn't trust it, might be phishing. Better stick to the legit stuff.
I searched for it and only found the hashraw site and this thread. Not much else out there. Unless you wanna right-click and save the page from there. But just because it doesn't make network requests when creating an address doesn't mean it's safe.