UFO2000 uses GPL license, its text can be read here: http://lxnt.info:888...k/trunk/gnu.txt
Also you can read some explanations here:
http://www.gnu.org/l...es/gpl-faq.html
http://en.wikipedia.org/wiki/GPL
But in a few words, GPL is a very permissive license, it allows you to make modifications to the original code, sell it, make business on it, but you are required to provide the sources of your modified work under the (which can be used by other people). That means, GPL licensed program is different from freeware. Freeware forbids commercial use, but GPL forbids adding modifications or using parts of sources without sharing them with everyone else.
Now about credits and copyright. Everyone who has contributed something to the project, should be mentioned in credits. Copyright is an universal thing and it exists independently of GPL or any other license (see http://www.gnu.org/licenses/gpl-faq.html#R...ClaimCopyright).
Anyway, that's my personal opinion, but I think that being too worried about putting copyright to every piece of code or arguing about who has made more significant contributions can be a source of many problems.
If you look at current copyright notice, it states the following:
Copyright © 2000-2001 Alexander Ivanov aka Sanami
Copyright © 2002-2005 ufo2000 development team
As you notice, it does not even have my name in it

Even now it is very hard to maintain AUTHORS file. Some contributions are more important, some are less important, some are just tweaks that even get removed from the later versions.
I certainly would not like to have any issues like this in the future:
1. Somebody who had contributed a minor change to the code claiming to be a core developer and a special notice in the AUTHORS file.
2. Somebody who had contributed a badly broken or buggy code (which had to be removed from the game later, or required lots of efforts from other people to fix it), claiming full copyright on this part of the game.
3. Somebody who had done major modifications to someone's else code, claiming full copyright on this part of code.
4. ...
Fortunately we have a version control system (SVN) and it stores all the changes for the last few years with appropriate comments (we can always find out who has added any improvement, when, and what files were affected). Probably the AUTHORS file can be changed, all the contributors listed alphabetically with a reference to a full SVN changelog?
As for me, I myself don't care much about being credited or not, developing the game is enough fun for me and watching the game improving every day is a good award itself. But other people, especially music and graphics contributors can can be worried about this much more. So we probably need (or don't need) to make some decision.
Comments and discussions are welcome.