Still a work in progress (like the original Black Mesa, they are adding one chapter at a time), but they just added Chapter 4 (total of 8). I've been playing it for a couple of hours and it looks amazing.
It's being treated as a mod for Black Mesa. You have to subscribe to the mod in the Steam Workshop, and then run a batch file to install the mod and create shortcuts. Instructions are on the page, but easy to miss:
-Subscribe to the mod in Workshop and wait for it to download.
-Go to your Library, click right mouse button on Black Mesa, go to "Manage" and click on "Browse local files";
-Go from current directory ("steamapps/common/Black Mesa" up to the "steamapps" folder;
-From this directory, go to "workshop/content/362890/2424633574";
-Once you locate the mod files, double click on "bshift_install.bat" and follow what it says.