Downloads
The latest version of the mod be downloaded from github.com.
Simply put the z-ratmod-v*.pk3
file into ~/.openarena/rat
(or %APPDATA%\OpenArena\rat
on Windows) and you should be able to load the mod from the OA main menu. You can also launch directly into the mod with openarena +set fs_game rat
from the command line (or adjust your desktop shortcut accordingly).
Source Code
You can find the source code for the mod hosted on github.com.
If you want to build the mod yourself, you should build it from the ratarena_release repository, which will include the assets.