Xash3D Engine

Latest version of the library is available at:
https://github.com/SDLash3D/xash3d

Orignal project: http://www.moddb.com/engines/xash3d-engine

Xash3D Engine is a custom Gold Source Engine rewritten from scratch. Xash3D
is compatible with many of the Gold Source games and mods and should be
able to run almost any existing singleplayer Half-Life mod without a hitch.
The multiplayer part is not yet completed, multiplayer mods should work just
fine, but bear in mind that some features may not work at all or work not
exactly the way they do in Gold Source Engine.

Xash3D Engine requires Half Life 1 SDK, you can find one at:
https://github.com/SDLash3D/halflife

Implying Half Life 1 SDK is cloned into /opt/halflife you should be able to
build Xash3D as:

$ mkdir -p xash3d/build
$ cd xash3d/build
$ cmake -DHL_SDK_DIR=/opt/halflife ..
$ make

The library is licensed under GPLv3 license, see COPYING for details.
CMakeLists.txt files are licensed under MIT license, you will find its text
in every CMakeLists.txt header.