Cougth* Hmm, 3rd time for this kind of topic?
oh well...
Q: What is the license?
A: Glest source code is GPL. For the data you can do whatever you want with it as long as you give the creator credit; This will work fine with nearly every open source license GPL/BSD/CreativeCommon. Only Public Domain will not work, as it has not credits.
Assuming it is the same license right now, not sure.
Does the GPL allow me to sell copies of the program for money?
Yes, the GPL allows everyone to do this. The right to sell copies is part of the definition of free software. Except in one special situation, there is no limit on what price you can charge. (The one exception is the required written offer to provide source code that must accompany binary-only release.)
Well, I am pretty sure John will give a better answer.
First, is is still of a GPL license? ...
Oh and also, even though you are talking about mods, I am pretty sure this being in the GAE board would be better...
Oh wait, I am not sure for what I just said...wait for John or the GAE team...