Change resolution before launch, choose software, Direct 3D, OpenGL or 3dfx OpenGL, enable 32-bit textures, launch Half-Life in windowed or fullscreen mode, change texture/model quality, enable EAX or A3D, disable Direct Sound, change sound quality; 11kHz or 22kHz, set custom heap size, change maximum decals, change maximum shells & smoke puffs (Counter-Strike) and more...

Note:
It support standard Half-Life, Team Fortress Classic and Counter-Strike (6.5 or newer)
Half-Life 1.1.0.1 or newer required.