VietDOOM is an upcoming total conversion mod for the original DOOM that's making good use of Brutal DOOM's additions and improvements to deliver an interesting first-person Vietnam-themed shooter.
The creator of the mod draws mechanics from both Brutal Doom and some of the older genre classics, like Medal of Honor (PS2), which seems like it will result in a very traditional sort of gameplay experience. Something you don't see all that often in 2019, for sure.
According to the creator, the aim of VietDOOM is for it to be a playable re-imagining of the story of Apocalypse now, but since this is DOOM, there will be a supernatural twist with demons and whatnot later down the line. There will be a sort of a "demo" campaign coming sometime soon, and it will include 10-ish missions of the vanilla kind.
Having said that, the author will eventually create a "proper" campaign for VietDOOM that's going to be way longer and more interesting. As you'd expect, there's no firm timeline to speak of, since this is - after all - a passion project through-and-through.
There's an awful lot of classic weapons planned for VietDOOM, and there will even be driveable vehicles - all of this running primarily on Zandronum, as per the author's recommendation. VietDOOM can run on the GZDoom sourceport as well, however, in a pinch.
Stay tuned for more info on this fascinating mod as it is announced.