(Disclaimer: I'm not a lawyer, just a free software enthusiast) > As long as the upstream is attributed, does the GPL3 explicitly prohibit this? If people are

(Disclaimer: I'm not a lawyer, just a free software enthusiast) > As long as the upstream is attributed, does the GPL3 explicitly prohibit this? If people are not displaying the GPL licence and attribution, that is obviously a violation, but this doesn't necessarily mean that. The GPL doesn't require attribution, merely that you comply with the terms of the GPL, in terms of making sure that any derived works are covered under the GPL. In fact, the GPL is incompatible with some versions of the BSD license because they require attribution. It's quite sensible to rename a project if you fork it so as to not violate the original developers trademark on the name (e.g. debian referring to their build of Firefox as Iceweasel) > I don't know enough about the GPL to know if you can "sell" GPL software (with sources and attribution, of course, which these might have) The GPL has no prohibitions against selling software covered under the GPL, as long as the software is licensed under the GPL and the source is made available. If selling GPL software were a violation of the terms of the GPL then companies like Redhat and Oracle could not sell their commercial distributions of Linux. This is why the FSF is careful to use the term "proprietary software" instead of "commercial software", since there is nothing in the GPL to prevent the software from being commercialized as long as it complies with the license.