Xash3D is the powerful independent open-sourced 3D-engine, aimed for high compatibility with GoldSource engine formats (maps, models, textures, sounds, entities etc.), but with the intention to be an advanced platform for modmaking or game development. Technically it has been built from a scratch, using as totally original ideas, as some ideas from other 3D-engines. Xash3D overcomes obsolete GoldSource engine's limits and provides for you a new quality of gaming experience and modmaking capabilities, as extended map, model, texture & sound formats with higher limits, possibility to implement custom renderers with dynamic lighting and other modern features. Xash3D is the easy-to-use base to play existing Half-Life mods & create something new, impossible with GoldSource. Years of development & testing allowed to make from Xash3D a perfect mix of high compatibility with common GoldSource standards & high openness to creative modmaking ideas.
It's not perfect (yet), but it's way better than choosing between OpenGL (framerate tank and sound stuttering on every dynamic light) and Software (genuinely looks like 100% ****).
The developer appears to be very active and has rebuilt GoldSrc to be bigger and better, utilizing the processing power you see on modern computers versus the Windows 95's and 98's.
Try it out, and if you don't like it in its current state, just verify your cache, no harm done.