In a nutshell... AC copyright

[Victor]

AssaultCube Reloaded is a fork of AssaultCube 1.0.4. They have two separate parts to deal with.

Source Code: 100% usable
zLib Licence. I don't claim that I made the original software. This is altered and plainly marked as "Reloaded". I provided attribution to AssaultCube.

Media: 99.9% (maybe add a few more nines) complete and usable
This one is a bit tougher, but was still easy to deal with. Most of their content was allowing reuse, and wasn't even created by AssaultCube. Some of them required attribution, which I fixed by adding readmes into the folder. For the "all rights reserved" ones, I left a notice so that they can come complain if they are the copyright holder.

Here is an example texture pack:

They are free to use for non commercial use.

How about another?

english:
copyright by arcitool
IMPORTANT: The offered files and images are meant to be freely downloadable. The files are not protected in any way, to allow high flexibility of usage and reproccession. Files may be altered in any way. Please mail us suggestions for changes, so we can assure future quality and replace files eventually.

All files and images may be used without restrictions in your projects.It is prohibited to offer those files as part of other texture packs or sell or distribute them in any other way without prior permission from arcitool.

You can't say that I can't use somebody else's work just because you used it. I assure you that most all (so far) of their complaints are false accusations. They're a bunch of idiots making invalid complaints. Just because AC used these copyleft textures, I cannot? What bullshit.

EDIT: 2 years later, and this is slightly updated... "Special Edition" is changed to "Reloaded".