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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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Sure, you can do that. But you need to give the source to everyone who gets the binary and there's nothing that stops those people from building the same software, except without the advertisement. – Joachim Sauer Jan 28 '13 at 16:45
Consider the case of taking someone else's GPL-licensed project, compiling it with ads, and distributing the result in a compliant way (i.e., with source code). That's legal, so there's certainly no reason why can't do the same with code that you wrote yourself. – apsillers Jan 28 '13 at 16:47
up vote 12 down vote accepted

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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Additionally, the advertisement code itself must be distributed under the GPL so someone could replace your advertisements with their own. – Craig Jan 28 '13 at 17:33
Good points that I'll make known to the dev team. – Volomike Jan 28 '13 at 20:20
Hmmmm, that would be an interesting test on the effectiveness of marketing. If a marketing team could take a little-known GPL'd project, slap some ad software on it, market the pants off it, would it be able to compete with the ad-free version? If they could bury the original to page two of google, and they're selling to windows (so apt-get is off the table), and you're feeling cynical about humanity... maybe. – Philip Jan 29 '13 at 14:19

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