I don't know about the gtk theme. Possibly part of the ElementaryOS project?

The HN skin is actually a Chrome extension called Hacker News Extension Suite.

https://chrome.google.com/webstore/detail/hacker-news-enhanc...

Hacker News Enhancement Suite chrome plugin. I've been using it for a few months, and it does a ton of handy little things.

Yep, both of you are correct HNES: https://github.com/etcet/HNES

Pretty much vanilla Elementary OS theme with Source Sans pro front.