The most interesting thing about this link, for me, is seeing that there's an open-source recreation of GoldSrc [0]? That's apparently been around since 2011 [1]? I'm stunned I haven't heard about this before. Very cool.
HN comment from a major maintainer here : https://news.ycombinator.com/item?id=38314427
Valve has confirmed that it violates the HLSDK EULA, too. At least for the original Xash3D release.