Probably a phishing site to steal username + password.
I wonder if it's someone's reverse-proxy to bypass censorship of the main site.
It does look like a live proxy rather than a copy/clone.
The responses have headers like "X-GitHub-Request-Id", which would be a pretty easy detail to forget if it were a copy.
To bypass the great firewall? Or possibly, to bypass country level restrictions on content blocks? You might have just outed some group in China.
Someone is going to have to be brave enough to login and see if their private repositories got cloned as well.
I have no private repo. It would suck if that too got cloned.
To steal passwords?
Looks like a social engineering attack of some sort.
Is this basically a MitM attack as a proxy?
Bob: Susan, remember not to make the GitHub staging site public by accident.
Susan: or what?
Bob: someone might me see it!
Susan: an obscure url like that? not a chance.
Bob: still, a small chance
Susan: and so what if someone sees it? it’s not like it will show up on the front page of Hacker News!
VirusTotal [1] is lighting up on that site. Do not click those links and I would remove the links from HN.
[Edit] HN Moderator removed it.
[1] - https://www.virustotal.com/gui/url/f298f1b568fccc7d942aa39c1...