Mod name: The Mission Pack
Also known as: Missionpack, The missionpack, Mission Pack
Instructions to make it work: Just select it from the "mods" menu. It is already included with your OpenArena installation.
Pretty much every feature of it (One Flag CTF, Harvester, Overload, the Nailgun, the Chaingun, the Prox Launcher, the Runes, the Kamikaze holdable and the Invulnerability forcefield holdable) is now an official feature of OpenArena itself.
The Missionpack mod comes together with the standard OpenArena installation: just select if from the main menu.
It still requires much work. If you want to help us with it (or in general, with OpenArena), please use our forum.