This is exactly what we ( http://linphone.org http://linphone.org ) do: we have a GPLV2 license that's used in many many open source projects, and we have a spe

This is exactly what we ( http://linphone.org http://linphone.org ) do: we have a GPLV2 license that's used in many many open source projects, and we have a specific license for commercial projects, for which we provide support and ability to not disclose the sources that our clients might modify. This kind of way to function give enough money to employ 10 people, and also secured a lot of new developments (encryption, video, etc.). Disclaimer: I'm just an employee, not the founder. I would advise him to switch to that kind of licensing, if he wishes to. There's no reason he shouldn't be able to live through his work.