I also wonder where is that tortoise texture from. Seems such a small thing to have the effort to create art for during development.
And of course there is quakeworld which is a complete fork with different net protocol, prediction, and commands. Example of new features is that skins can be downloaded on the fly, you no longer needed skinpacks.
There are many good source ports of quake, I always liked darkplaces but it intentionally and willfully tries to push improvements so not really for purists. There is stuff like fitzquake/quakespasm that stays much closer to vanilla quake and if you like quakeworld ftequake.
The earliest doom variants once the source code released started adding features that weren't faithful to the original dos version 1.9.
Even Boom which was a pretty conservative codebase that focused on limit removal for level editing added weird things like weapon recoil pushing the player back when you shoot a weapon.
So chocolate doom's name is wordplay on "vanilla doom" - it's the version of doom we all played in the 90s just updated with current i/o libraries (libSDL) so it can run on modern platforms.