Gunman Chronicles is a futuristic first-person shooter computer game using the Half-Life game engine. It was originally planned as a total conversion for Quake; it then switched games to Quake II, followed by another switch to Half-Life, before being spotted by Valve Software and released as a stand-alone retail product in 2000.
Very good sci-fi standalone Goldsrc game ever. Even design and excellent atmosphere. Good AI and mini-quests that make the gameplay more versatile. Love it.