Unstable release
You can check out the latest unstable release of GTK-Doc using Git.
git clone git://git.gnome.org/gtk-doc
For more information on this, see the instructions on how to use the repository
Stable release
GTK-Doc is available here:

You can check out the latest unstable release of GTK-Doc using Git.
git clone git://git.gnome.org/gtk-doc
For more information on this, see the instructions on how to use the repository
GTK-Doc is available here: