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Hi,
Look this article, maybe it's clear your doubts. Well, my idea about it is: You can improve features, modules and much more and those are considered customization, but you can't sell Xoops.
I have a little company and i distribute Xoops, but i'm selling just services for customization, e.g: Supply Chain module or Oracle integration.
http://www.gnu.org/licenses/gpl-howto.html
Well, if i'm not right, please someone alert me.
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