We’ve been thinking of using GPL components to make a GPL application, and freely give it away. We then want to use that as a loss-leader. In that free application, where even the source code is available, we plan to have an advertisement for some payware. The payware would be for functionality that is completely different than the free application. For instance, the freeware would be like a checkbook application, let’s say, but the payware would be a virus remover utility that people try out and then can pay for, and is closed-source, binary.
Does the GPL permit one to build an application that has a payware advertisement on it?
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The GPL allows that.
However, the GPL requires that you give the source to everyone that gets your GPL application and allows anyone to modify and redistribute your code. If the GPL application you release is useful, it won’t take long for someone to take your source, remove the ads, and redistribute the application. And, presumably, the vast majority of users will prefer the ad-free version rather than the version that you are distributing with ads. Unless you have some distribution channel that is substantially better than the distribution channel of whoever decides to fork your app and distribute the ad-free version, it seems unlikely that your GPL application would attract many users.
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