And no, this is not a thread for downloading them as I'm not sure about how legal they actually are, since they are ROMS after all.
But anyway, back in February of 2008, a guy named drx released a massive amount of Genesis/Mega Drive, Gamecube, Sega 32X, and Mega CD/Sega CD prototypes. Among these were 16 builds of Doom 32X.
Yes, I know what you're thinking. "Farts and Zippers" version. Well, the earliest prototype is completely silent and the second one features a primitive (and possibly better) version of "At Doom's Gate.
The earliest two prototypes also use the PC textures and geometry before using the Jaguar layouts in builds after that. They were also fullscreen. Unfortunately, it causes performance problems as the game is kinda choppy at points. In addition, both of these protos cannot be completed because the game freezes after the level 5 end switch is pressed.
I've actually started a list of changes between the prototypes here on this Doomwiki page: http://doomwiki.org/wiki/Doom_32X_Development
There's also a screenshot gallery at the bottom of the page you can look at.
This list is far from done though I'm afraid. I still have to dig in more thoroughly. Of noting, there are actually four prototypes dated AFTER the release. Three of these go under the name "DOOM RR" whatever that means. These four have no noticable differences but some bugs may have been fixed. Needless to say, if this was a revision, SOA quickly canned the project.