Xash3D FWGS Engine (Fork) 
Original project: Xash3D Engine on ModDB
Original codebase we're based on: Xash3d FWGS (Old) on GitHub
Xash3D Engine is a custom game engine rewritten from scratch.
Xash3D is compatible with many of the GoldSource games and mods
and should be able to run most of existing singleplayer Half-Life mods without a hitch.
The multiplayer is working, but network protocol isn't compatiable with the GoldSource Engine
multiplayer mods should work just fine, but keep in mind that some features may not work at all
or work not exactly the way they do in the GoldSource Engine.
Xash3D-NG is a fork of Xash3D FWGS Engine (Old one) which itself is based on Xash3D by Uncle Mike, this fork aims on improving and bugfixing the original FWGS codebase.
License
The library is licensed under GPLv3 license, see COPYING for details. CMakeLists.txt files are licensed under MIT license, you will find it's text in every CMakeLists.txt header.