DashEngine VS BetterSADX

There's literally sites devoted to Sonic fangames, and open source Sonic games/engines. Hell, one of the Headcannon devs has their fangames available, after making a game published by Sega.

So, SADX is a bad port of SA1, on GameCube and especially on PC, principally because of the hugely downgraded lighting systems, weird decisions made with the new textures that change the look of a lot of stages, and character models that don't conform to the original design language, alongside a lot of other small stuff (all of which you can read about in too much detail here if you haven't heard any of it before). You can basically revert SADX to SA1's textures, models, and a remarkably faithful facsimile of the lighting engine using either BetterSADX or the SADX Mod Installer. People recommend the SADX Mod Installer as it's more modern, but I found that I couldn't get the installer to point to the right install directory when I was running it through Proton, so I used BetterSADX instead. That'll install a suite of mods that basically revert the game to the original Dreamcast version, along with downgrading the Steam version of SADX back to the 2004 port that's less broken at its base and far more moddable. The end result is, in my view, a huge improvement over the frankly terrible base PC port, and essentially exactly what the SA1 developers originally put out, compared to the baffling decisions made with the port.