From Quake Wiki
A majorly popular game based on Quake's game code...
It was mildly popular since its November 1998 release but it skyrocketed with the release of Counter-Strike in 1999. This highly boosted sales of the game and quickly taken the throne of the most popular multiplayer game in 2000.
In 2013 an early prototype of the game was released. The Cutting Room Floor wiki has details: https://tcrf.net/Proto:Half-Life_%28Windows%29/September_1997_Prototype
- Skeletal model system, with 4096 triangles maximum per surface and 1024x1024x8 maximum texture resolution and depth, and optional environment mapping for textures
- A sound DSP with reverb, chorus and echo effects for software-mixed environmental audio without needing EAX.
- Colored, radiosity lighting for maps, compiled with a fork of QRAD.
- HLBSP supporting colored lighting, variating hull sizes and external textures (also supports internal textures like Quake, but not officially)
- Water waves and transparency
- Material system for walls and floors to define impacts and footstep noises
- Particle system with trailing particles
- Beam system for beam effects including support for depthWrite fades, with shapes like straight beam, lightning noise and cylindric shockwaves
- Sound sentence sequences, for stringing a bunch of WAV files in an order to construct a sentence (i.e. Speech of announcer, marines, etc)
- Simple lip sync
- PROGS are in DLL form divided into cl_dll (for client-side) and dll (for server-side), and as such, require Microsoft Visual C++ 6 to compile.