Xonotic 0.7 Released!

What Mr. Bougo (when did you add that point there???) tells, is that the codebase of Overkill is actually part of Xonotic officially too, but not the media. You can try contacting Morphed or tZork to get the pk3 too that you need to play it offline, also they can help you how to start your own local server.

Oh, I wasn't aware of the media being outside of the server. It kind of makes sense, considering the licensing... Although there's no requirement for branches to be GPL-compatible until they are subject to a merge request.

Anyway, s/he probably has the pk3 already, in dlcache!