Say someone made software, put it up on GitHub under the GPLv3 License, but then had an EULA that is not supplied with the binaries on GitHub, do you have to follow the EULA, or the GPL? And do they have to supply the source code with the binaries?
You can certainly distribute code under GPL freely (e.g. via github) while selling licenses (EULAs) with additional rights (create closed derivatives, for instance) using other channels. You just have to make sure you have all rights to whatever you license separately (i.e., you have to get everybody who contributes changes to the public version write over the rights to you if you want to incorporate it into the EULAed package). This is usually called a CLA (Contributor Licence Agreement) to be formally accepted by any contributor before you integrate the contribution,