There is a repository for this, and that, and everything -- the incubator: https://git.savannah.gnu.org/cgit/hurd/incubator.git/.

As the README file in the master branch says, the development of the various software happens in separate branches.

Handling branches with git-new-workdir

git-new-workdir is a contrib script provided with the git distribution (on Debian systems, in /usr/share/doc/git/contrib/workdir/git-new-workdir); it allows to create a new subrepository of a git repository, tracking one of its branches, usually as a subdirectory of the current repository.

The advantage of using it for incubator is that only one clone is needed, and it can be possible to work simultaneously on many branches (instead of only on the current branch of that clone).

Let's start checking out the incubator repository:

$ git clone git://git.savannah.gnu.org/hurd/incubator.git
$ cd incubator/

Assuming we now want to follow the development of the tarfs/master branch: we follow this branch:

$ git branch -t tarfs/master origin/tarfs/master

Then now setup a local subrepository tarfs following it; we will create it as subdirectory of incubator (first parameter for git-new-workdir) for simplicity, but can be created anywhere else:

$ git-new-workdir . tarfs tarfs/master

After this, a new tarfs subdirectory appears, which represents the tarfs/master branch. You can normally work on this new repository as usual.