It’s a stand alone project building off of the 2001 build’s leak, trying to turn it into a completed game.
The download includes the leaked original content as well if you want to compare. The original content isn’t really playable as anything but novelty, since it’s more like the skeleton of a game than a game. The project has made strides in all aspects to turn half finished, often unpopulated locations into actual game levels. Pigcops are back, Duke’s model is improved, more voice acting included, level design with scripted encounters. Lots of stuff.