[0] https://github.com/fwgs/xash3d-fwgs
[1] https://www.moddb.com/engines/xash3d-engine
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.